In recent years, the issue of “being mentally ill” has become a major concern of public opinion. seems to be a common phenomenon. In order to alleviate the public’s concerns, this article briefly introduces how the diagnosis of mental illness is made. Psychiatry is a branch of clinical medicine. In brief, the conventional process of diagnosing mental illness includes the following three steps: (1) A professionally trained physician obtains information about the patient’s illness, which includes (1) A complete medical history of the patient by interviewing the patient and those who know about the patient’s condition; (2) Through a comprehensive and effective mental status examination, the medical practitioner analyzes and summarizes the patient’s mental symptoms; (3) Through physical examination and a physical examination, the patient’s psychiatric symptoms are analyzed and summarized. (3) Systematic assessment of the patient’s somatic condition through physical examination, laboratory tests and brain imaging and other examinations. (2) Conduct a comprehensive analysis and judgment of the information obtained about the patient’s illness, and arrive at a diagnosis of mental illness based on a common diagnostic system. 3. Observe and follow up the patient to make necessary corrections to the diagnosis and treatment. The above three points are the common medical diagnostic procedures, and what is special in psychiatry is the special medical history inquiry, mental status examination and assessment. First, some people believe that there are no objective biological criteria for judging mental illness, and that the presence or absence of mental illness depends on the doctor’s mouth: “If you say you are sick, you are sick”. It is undeniable that the current diagnosis of mental illness may be interfered with by certain subjective factors, but the diagnosis of mental illness is generally scientific and objective because: First, abnormal mental activities are manifested through outward behavior such as speech, writing, expression, and action behavior, which are called mental symptoms. Through the generalization and summary of many psychiatrists in ancient and modern times, psychiatry has formed a special discipline for studying mental symptoms and their generation mechanism called symptomatology of mental disorders, also called psychopathology. All doctors analyze and evaluate the mental activities of each patient according to the knowledge of psychopathology, discover and summarize the mental symptoms, and thus lay the foundation for diagnosing mental diseases. Secondly, after more than 100 years of development, psychiatry now has an international diagnostic system, namely the International Classification of Diseases and Diagnostic Points (ICD) and the Diagnostic and Statistical Manual of Mental Disorders (DSM), and China has also developed the Chinese Classification and Diagnostic Criteria of Mental Disorders, taking into account international experience and the actual situation in China. Psychiatrists who have undergone rigorous training in psychopathology can reach a consistency of more than 85% in the diagnosis of psychiatric symptoms, and in turn, the consistency in the diagnosis of psychiatric disorders based on the same diagnostic criteria is quite high, even no less than the consistency in the diagnosis of diabetes and coronary heart disease made by clinicians. Another misconception is that doctors use “not admitting illness” as an important or only criterion for diagnosing mental illness, as one newspaper even described, “A frightening situation is that every normal person faces the possibility of being institutionalized at any time by someone with an ulterior motive. The more you say you are not mentally ill, the more you are considered mentally ill. In fact, this is a complete misunderstanding. All diagnostic criteria do not include an acknowledgement of illness (self-awareness), and self-awareness is only used to determine the outcome and prognosis of patients who have been diagnosed with a serious mental disorder. Self-knowledge is not very useful in determining the diagnosis of mental illness. It must be noted that in daily psychiatric medical practice, the basic assumption of psychiatrists is that family members or other informants will not provide false information on their own initiative because of their interests. This phenomenon exists in all fields of medicine. According to the Law on Medical Practitioners, the physician must personally examine and examine the patient before making a diagnosis. For a variety of reasons, this procedure has failed to receive adequate attention in occasional cases, and misunderstandings have arisen. As with all medical disciplines, misdiagnosis or inconsistent diagnosis of mental illness is inevitable. There are many reasons for this phenomenon, including incomplete collection of information about the patient’s illness, the changing nature of mental illness itself, etc. Medical practitioners need to take a number of steps to reduce this: 1) to obtain as comprehensive information as possible about the patient’s illness; 2) to strictly follow diagnostic criteria; 3) to use standardized diagnostic tools to improve diagnostic consistency, etc. In addition to improving the quality of our own psychiatry, it is important that we follow the diagnostic procedures. We look forward to the emergence of a mental health law that will improve mental health for all, protect the rights of normal people and people with mental illness, and reduce discrimination and prejudice against people with mental illness.