1, biochemical factors: mainly refers to the occurrence of depression may be related to a decrease in the concentration of the brain synaptic gap neurotransmitters 5-hydroxytryptamine (5-HT) and norepinephrine (NE). 2.Psycho-social factors: The sudden occurrence or long-term persistence of various major life events can cause intense or (and) persistent unpleasant emotional experiences, leading to depression. 3, genetic factors: genetic epidemiological survey of a large sample of the population 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 other relatives, which is consistent with the general rule of genetic diseases.