Depression is a common mood disorder that can be caused by a variety of reasons, with significant and persistent depression as the main clinical feature, and the depression is not proportional to its situation, and in severe cases, suicidal thoughts and behaviors can occur. Most cases have a tendency to have recurrent episodes, most of which can be relieved with each episode, and some can have residual symptoms or become chronic. 1, genetic factors: a large sample of population genetic epidemiological survey shows that the closer the blood relationship with the affected person, the higher the probability of the disease. The probability of first-degree relatives having the disease is much higher than that of other relatives, which is consistent with the general rule of genetic diseases. 2, biochemical factors: catecholamine hypothesis: mainly refers to the occurrence of depression may be related to the decrease in the concentration of neurotransmitters 5-hydroxytryptamine (5-HT) and norepinephrine (NE) in the brain synaptic gap; due to the use of many antidepressants, such as selective 5-hydroxytryptamine reuptake inhibitors (SSRI) or selective 5-hydroxytryptamine and norepinephrine reuptake inhibitors (SNRI), etc. Although the concentration of these neurotransmitters in the synaptic gap of the brain rises quickly, the antidepressant effect generally still takes about 2 weeks to take effect, hence the hypothesis of increased sensitivity of 5-HT and NE receptors (hypersensitivity); 3. Psycho-social factors: the sudden occurrence of various major life events, or their long-term persistence can cause intense or persistent unpleasant emotional experience, leading to depression. According to the third edition of the Chinese Classification and Diagnostic Criteria of Mental Disorders, depression can be classified as mild depression or major depression according to the degree of impairment of social functioning; depression can be classified as depression without psychotic symptoms or depression with psychotic symptoms according to the presence or absence of psychotic symptoms such as hallucinations, delusions, or stress syndrome. Depression is divided into first-episode depression and recurrent depression according to whether there has been another depressive episode before.