There are rich contents of TCM diagnosis, and tongue diagnosis is one of the important contents of TCM diagnosis. Tongue diagnosis, also known as tongue examination, is a unique diagnostic method that has gradually developed with the development of Chinese medicine, and has become the examination routine for almost every Chinese medicine practitioner. With the progress of society, economic development, people’s health care awareness gradually increased, tongue diagnosis as a health detection, diagnosis of disease technology, will enter thousands of households, for the benefit of mankind. Tongue is a mirror of human health. According to Chinese medicine, the tongue has a close connection with the internal organs, mainly through the circulation of the meridians. The tongue is the seedling of the heart, the outer germ of the spleen, and the moss is the steam of the stomach qi. Physiologically, the essence of the internal organs can reach the tongue through the meridian connection, playing its role of nourishing the tongue body and maintaining the normal functional activities of the tongue. In this normal state, the tongue is light red, red and moist, not shallow, not deep, red and alive, covered with thin white moss, not dry and not wet. Pathologically, the pathology of the internal organs must also affect the changes of the essence and be reflected in the tongue. In modern medical terminology, it means that when the body suffers from various diseases, it will affect the endocrine function, blood composition and changes in nerve conduction and digestive function, which will be reflected in varying degrees from the tongue image. Therefore, the tongue is known as the external symptoms of the internal organs and can show the changes of the internal environment of the body. Cao Bingzhang’s “Guide to Tongue Identification” says: “Identification of tongue quality can identify the deficiency of the internal organs, and inspection of tongue moss can detect the depth of six perversions.” That is to say, the clinical disease can be observed from the tongue image in terms of its severity and urgency, as well as its fortune and fate. From the point of view of biological holographic law, any part is similar to the microcosm of the whole, and the tongue is no exception, so the former people have the tongue body should be the internal parts of the said. The basic rule is: up to wait for the top, in order to wait for the middle, down to wait for the bottom. Observing the changes of tongue image can help to identify diseases, analyze the changes of disease mechanism and evaluate the effect of clinical treatment. It is important to note that complex diseases sometimes have a variety of false signs or similar signs, that is, one tongue image may reflect multiple diseases, and the same disease may have two or more tongue images. The tongue is an important objective basis for the process of disease change, but it is not a necessary clinical manifestation. When analyzing the tongue, it should be combined with pulse diagnosis and other diagnostic methods to have clinical significance. To look at the tongue to diagnose the disease, we should pay attention to the method. First of all, the light should be good, with sufficient and soft natural light is preferred. For the body position, the general requirement is sitting posture, serious illness can also be lying down. To open the mouth as much as possible, naturally stretch the tongue out of the mouth, fully exposed. Pay attention to the influence of some factors. Diet often causes changes in the shape and color of the tongue. For example, certain foods or drugs can stain the tongue, called “dyed moss”, and sometimes can also affect the quality of the tongue changes. The application of adrenocorticotropic hormone and thyroid hormone can make the tongue more red; tumor patients receiving chemotherapy usually have less or drier tongue moss; long-term application of broad-spectrum antibiotics can make the tongue yellowish-brown, grayish-black or no tongue moss; drugs such as compound licorice tablets and golden voice throat can stain the tongue moss black; safranin and riboflavin can stain the tongue moss yellow; eating peanut rice can make the white moss thicker and greasier; eating green vegetables such as Cucumber, fennel, etc. can be dyed green moss; children eating chewing gum, cold food or drinks are also easy to dye the tongue into various colors. Normal tongue like, often with different seasons and different times and slightly change. Such as summer heat and humidity, tongue moss more thick, or a light yellow; autumn dryness when the order, moss more thin and dry; winter cold, tongue often moist. For example, the tongue moss is thick in the morning, but thinner after eating during the day; when you just wake up, the tongue color can be seen as dark and stagnant, but after activity, it often becomes red and active. The content of tongue diagnosis is very rich, mainly including looking at the tongue body and looking at the tongue moss. The tongue body mainly observes the tongue god, tongue color, tongue shape and tongue attitude. A normal tongue should be angry and lustrous, that is to say, the so-called glory of the red live, this is a god. Even if there is disease, it is still a good wait. If it loses its luster, it is not good. Therefore, the presence or absence of the god of the tongue reflects the vitality of the internal organs, qi, blood and fluid, and is related to the prognosis of the disease. The color of the tongue is light red when it is normal. When the body is infected with disease, the epithelium of the mucous membrane of the tongue becomes hypertrophied or atrophied and thinned, etc., which can cause changes in the color of the tongue. Tongue color lighter than normal, or even no blood color, called “light white tongue”, the main deficiency, cold evidence, mostly seen in a variety of anemia and severe malnutrition patients. Long-term chronic blood loss or acute hemorrhage caused by various reasons can also appear pale white tongue. Clinically, the degree of hemoglobin reduction is judged by the different severity of the pale white tongue. Deeper than normal called “red tongue”, mostly seen in hot evidence, such as wind and fever colds can be seen on the tip of the red tongue (on to wait on). Deeper than bright red is called “vivid red tongue”, vivid red tongue is mostly due to the gradual development of the disease, from the bright red tongue, common in infectious diseases and chronic wasting diseases, such as Chinese medicine said warm disease heat such as Ying blood that can be seen vivid red tongue. In some chronic diseases, the appearance of reddish-red tongue is often a bad precursor, such as acute exacerbation of chronic obstructive pulmonary disease patients appear reddish-red set, and the tongue coating is completely absent, suggesting true yin damage, heat and toxicity, treatment will be very difficult. Tongue color such as red with green or blue is called “blue-violet tongue”, and blue-violet tongue is more serious than red-red tongue, the ancestral medicine will describe this tongue as lung Qi has been extinguished to indicate the severity of the disease. Modern medicine believes that the blue purple tongue occurs in irreversible microcirculatory shock, or some infectious diseases and high fever period and blood in a hypercoagulable state, blue purple tongue is also related to respiratory failure, such as chronic obstructive pulmonary disease, bronchial asthma caused by respiratory failure, etc.. Tongue shape is the shape of the tongue. Tongue shape has old and young. Old is the rough texture of the tongue, the shape of the firm and old, generally seen in the actual evidence. Young is a delicate texture of the tongue, the shape and color of the floating fat and tender, generally seen in the deficiency of evidence. Tongue enlargement, full mouth full mouth, or even can not close the mouth, can not be retracted, known as swollen tongue. There are three causes: one is the heart and spleen have heat, the tongue is bright red and swollen, and even with pain; one is good at drinking, and the disease of warm heat, the tongue is purple and swollen; one is due to poisoning and blood clotting, the tongue is swollen and blue and dark. Tongue body thin and thin, called thin thin tongue. Mainly qi and blood deficiency and yin deficiency fire. Thin, thin and light-colored is mostly deficiency of both qi and blood. Thin, thin and red-red dry, mostly yin deficiency fire, fluid depletion. The tongue surface has more or less, varying depths, various forms of obvious cleft grooves, called cracked tongue. Mostly seen in the following cases: one is yin deficiency, such as fever for a longer period of time, not much diet, and those who use sweating drugs to retreat easily; one is blood deficiency without moistening, such as some patients with chronic wasting diseases; one is spleen deficiency with damp invasion. This tongue shape is also seen in some healthy people. Traces of teeth are seen on the edge of the tongue body, called tooth mark tongue or tooth mark tongue. Sometimes it is seen together with a fat tongue, which is mostly due to spleen deficiency or qi deficiency. Tongue posture refers to the dynamics of the tongue body. If the tongue body is stiff and straight, with no movement, so that the speech is sluggish, it is called “strong tongue”. It is a symptom of heat entering the heart, high fever injuring fluid, internal obstruction of phlegm, stroke or aura of stroke. It can be seen clinically in various kinds of encephalitis, meningitis and acute cerebrovascular disease. The tongue body is weak, unable to flex and extend, impotent and ineffective, called “impotent and soft tongue”. If the tongue is light and impotent after a long illness, it is mostly due to deficiency of both qi and blood; if the tongue is dry and red and impotent after a new illness, it is due to heat and fluid injury; if the tongue is vivid and impotent after a long illness, it is due to extreme yin deficiency. It is mostly seen clinically in acute fever and cerebrovascular disease. In patients with alcoholism, the tongue may tremble and shake and cannot move on its own, which is called “trembling tongue”. If the tongue is tilted to one side, it is called “skewed tongue”. The main stroke or stroke aura. Tongue coating includes moss color and texture. The color of the moss is white, yellow, gray, black and so on. There is a thin layer of white moss on the normal tongue, laying flat on the surface of the tongue, evenly granulated, dry and moist to medium. In addition to normal people, white moss can also be seen in patients, which is a milder and better prognosis of the tongue, mostly seen in superficial evidence and cold evidence. Since the external evil has not yet spread to the inner part of the tongue, there is often no obvious change in the tongue moss, which remains a normal thin white moss. From the modern medical point of view, the formation of yellow moss is related to inflammation and infection, but also related to fever, lack of water in the body, gastrointestinal dysfunction and local inflammatory exudation of the tongue, such as chronic gastritis, gastroptosis and other common. In Chinese medicine terminology, yellow moss is the main evidence of internal and heat, and it is different from light yellow, soft yellow, deep yellow and burnt yellow. Gray is light black, gray moss is the main evidence of internal heat, commonly seen in the evidence of internal heat, also seen in the evidence of cold and damp. Grey moss and dry, mostly heat incandescence injury, seen in external heat; or Yin deficiency fire, common in internal injury miscellaneous diseases. Grey and moist moss is seen in internal stagnation of phlegm and drinks, or internal obstruction of cold and dampness. Black moss is the manifestation of high fever, dehydration, acute and chronic inflammation, toxin stimulation, central nervous system dysfunction, mycobacteria and other diseases, clinically seen in acute purulent infections such as sepsis, acute cholecystitis, etc. Chronic diseases such as uremia, chronic bronchitis can also appear black moss. The appearance of black moss often indicates a serious degree of illness and a poor prognosis. When examining it, we should also pay attention to distinguish the illusion caused by drugs or food staining. The quality of moss refers to its thickness, moistening and dryness. Thickness and thinness: The thickness of the moss is based on the criteria of “seeing the bottom” and “not seeing the bottom”, i.e. the moss that can be seen through the tongue is “thin moss”, while the moss that cannot be seen is “thick moss”. “thick moss”. Thickness can measure the depth of the evil Qi. Thin moss is mostly for the beginning of the disease, the evil is on the surface, the condition is light; thick moss shows that the evil is strong and has spread to the inside; or there is stagnation in the stomach and intestines; or there is phlegm and dampness. The thicker the moss is, the more prevalent the evil is and the more serious the disease is. However, the formation of tongue moss reflects the presence or absence of gastric qi. Although the tongue moss is thick, it indicates that gastric qi is still present on the side, while less moss often indicates that the body is deficient in positive qi, and no moss is a big deficiency of gastric qi, lacking the opportunity to develop. If there is irregular flaking of tongue moss on the surface of the tongue and the flaking area is smooth and moss-free, it is called flower flaking moss, which mostly belongs to the deficiency of gas and yin of the stomach, and if there is also greasy moss, it means that phlegm and dampness have not been transformed and the positive qi has been injured. Moistening and dryness: the changes of fluids can be understood. Moist moss indicates that the fluids in the disease have not been injured. Dry moss is mostly seen when heat has injured fluid. Observation of the tongue should combine the moss color and moss quality, not to be biased. In conclusion, the tongue image in Chinese medicine has its physiological and pathological basis, and the tongue image has some connection with the nature of the disease and its development. However, tongue image only reflects one side of the physiology and pathology of the organism, so when analyzing the tongue image, we should have a holistic view and should not generalize the whole picture, but should pay attention to the relevant theories of Chinese medicine, not only to achieve a comprehensive diagnosis of tongue quality and tongue moss, but also to achieve the four diagnoses together. In today’s soaring technology, further qualitative and quantitative analysis of tongue image by computer and modern information technology, and establishment of objective and unified identification standard of tongue diagnosis will provide more effective guidance for clinical research of Chinese medicine, promote the development of basic and clinical research of Chinese medicine and the exchange between Chinese and Western medicine, and play an important role in promoting Chinese medicine to the world. Moreover, with the development of Internet technology, remote diagnosis and treatment has become an important means of contemporary medical treatment, and the modernized research results of tongue diagnosis will provide methodological and technical support for this technology.