Medical psychology believes that it is necessary to maintain a unified view of mind and body in the matter of human health and disease. According to this view, diseases can be divided into three categories: First category of diseases: the causative factors act directly or first on the brain, and the pathological changes are mainly in the brain, producing obvious psychiatric symptoms. This group of diseases mainly includes some diseases related to brain damage in neurology and the vast majority of diseases in psychiatry. In these disorders, psychological factors are sometimes the main causative and sometimes predisposing factors. The second category of diseases: the causative factors act directly or indirectly on the organs of the somatic systems other than the brain, and the pathological changes occur mainly in the organs, but the patient’s symptoms are characterized by the prevalence of psychological disorders, and some of them also present varying degrees of psychiatric symptoms. This group of diseases includes most of the diseases of clinical departments except brain diseases of neurology and psychiatric diseases. The third category of diseases: the causative factors are mostly physical and chemical factors acting directly on various organs of the body, and the pathological changes are obvious local organ or tissue damage, and the psychological state of the patient after the disease affects the course of the disease, and some also produce obvious psychological disorders. For example, sudden trauma, burns, poisoning, etc. The causative agent of infectious diseases is a living pathogen, and the process of its occurrence and development in the human body is fundamentally different from that of non-infectious diseases. Some scholars have done research on patients with viral hepatitis B, one of the common infectious diseases, and found that such patients had more socially problematic life events before the disease, and there were mostly significant differences compared to healthy controls. However, when compared to non-hepatitis medical patients (mainly psychosomatic), social problem life events were less and significantly different than the latter. This suggests that psychosocial factors due to life events, although having some influence on the development of hepatitis B, are much less influential than in patients with psychosomatic diseases. Therefore, it is inferred that psychosocial factors are only contributory factors in the development of hepatitis B, and the main cause of the disease is still the biogenic effect of the hepatitis B virus.