Colorectal cancer is a common tumor that seriously threatens human health and life, and is the most common malignant tumor in developed countries such as Western Europe and North America, and ranks 4th in China, with a rising trend recently. Among them, rectal cancer accounts for more than half of colorectal cancer. At present, the treatment of malignant tumors is still mainly surgical resection. Early detection of rectal cancer is clinically important, which not only affects the success rate of surgical resection, but also has a close correlation with the prognosis (postoperative recurrence rate and survival rate). How to detect rectal cancer at an early stage is especially important. The most common clinical symptom of rectal cancer is blood in stool, which is usually dark red or bright red in color. It is usually dark red or bright red in color. It is interspersed with mucus or pus, and sometimes it can be interspersed with blood clots. It is often misdiagnosed as hemorrhoid and delayed treatment, which aggravates the disease, and those who come to the clinic are mostly in the middle and late stage, which is very difficult to treat. Hemorrhoid bleeding is mostly bright red, bleeding mostly after defecation, dripping or spraying out, blood and stool do not mix; while rectal cancer bleeding is mostly mixed with stool, and accompanied by bad odor. Another symptom of rectal cancer is the change of bowel habits. In early stage of rectal cancer, the number of stools increases, the stools are thin or mucus stools, or the anal swelling is uncomfortable, and there is a feeling of incomplete bowel movement. The number of stools is several times to ten times a day, and the volume of stool is reduced, mostly mucus or pus and blood. Tumor enlargement may lead to thin stool, deformation and difficulty in defecation. Mucus and blood stool and anal swelling can be easily misdiagnosed as dysentery or other intestinal inflammatory diseases. When rectal cancer develops further and invades the skin of anal canal, anal pain will appear; when it invades sacral plexus nerve, there will be severe and persistent pain in rectum or sacrococcygeal area, and it will radiate to the lumbar area, perineum or inner side of lower limbs. When the tumor enlarges and obstructs the intestine, it causes obstruction. Long-term bleeding leads to anemia and cachexia in the late stage. If you have the above mentioned symptoms, you should seek medical attention immediately and make a comprehensive and careful examination, the common examination methods are as follows 1.Anal rectal diagnosis: Rectal diagnosis is a simple and extremely effective method for the diagnosis of lower and middle rectal tumors. Usually in lateral or thoracic knee position, the rectal mass can be palpated about 7-8cm from the anal verge. 70% of rectal masses can be palpated by finger diagnosis. Through finger palpation, we can find out the location, size, shape, texture of the tumor, whether there is a tip, the activity of the base, the depth of infiltration of the mass, and the relationship between the base and the surrounding organs. After retracting the finger, pay attention to whether there is pus and blood in the finger sleeve. Do not press the tumor roughly and forcefully when doing finger diagnosis to avoid tumor rupture and bleeding and tumor spreading. 2.Endoscopy: through endoscopy, it can directly observe whether there are lesions such as congestion, edema, ulcer and neoplasm in anal canal, rectum and colon, and understand the location, size and nature of lesions, which is of great value for early detection of lesions, especially early colorectal cancer and precancerous lesions. Commonly used endoscopes are anorectoscopy, sigmoidoscopy and fiberoptic colonoscopy. Once a suspicious mass or ulcer is found, a biopsy should be taken for pathological examination. If the pathology is negative but the clinical suspicion is high, the examination should be performed twice or more. 3.CT or MRI: CT or MRI examination can clarify the size and location of tumor, the depth of invasion of intestinal wall, the relationship between tumor and surrounding adjacent organs, the presence of surrounding lymph node enlargement, and help to judge the possibility of surgical resection of tumor before operation.