The prognosis of psychiatric disorders is closely related to whether patients receive timely and correct treatment. Under current technological conditions, it is difficult to obtain biological indicators with good sensitivity and specificity for early diagnosis of depression, and therefore early diagnosis depends on timely detection of early symptoms of depression. Depression is manifested at three different levels, namely depressed state of mind, syndromes with depressive symptoms, and depression meeting internationally recognized diagnostic criteria. A depressed state of mind refers to the presence of sadness, unhappiness, or a poor state of mind that lasts for a period of time. Symptoms of anxiety/depression syndrome include sadness, unpleasant emotions, guilt and feelings of worthlessness. Depressive state of mind, depressive syndrome and depressive disorder reflect the three levels of depression. Based on this evolution, it is certain that depressive state of mind is an important marker or signal of a depressive episode and that people who experience depressive state of mind are more likely to experience a depressive episode in the future. It is worth noting that: depression in Chinese people shows more somatic symptoms (easy fatigue, headache, lack of appetite, sleep disturbance, low libido), while complaints of painful experiences (low mood, decreased self-confidence, reduced interest) are relatively less frequent, especially in the early stages of depression, and depressed individuals in China may show more symptoms such as autonomic dysfunction. Such a fact makes the early diagnosis of depression very difficult. Dryman et al. (1991) conducted a one-year follow-up study and found that major depressive episodes in adulthood were mainly associated with pre-existing symptoms such as feelings of worthlessness, inattention, loss of libido, sleep disturbance (more common in women), fatigue and weakness (more common in men). （Wilcox et al. found that persistent dysphoria, loss of pleasure, worthlessness, and suicidal ideation in adolescence were precursors to major depression, and that chronic loss of pleasure and worthlessness in particular were good predictors of depression; while Lang et al. found that self-reported physical symptoms (e.g., sleep disturbance) were more common than those of depression. (e.g., sleep disturbances) were more accurate predictors of depression than cognitive impairments (e.g., suicidal ideation). Stressful life events are strongly associated with depression. Negative life events, such as widowhood, divorce, marital discord, unemployment, serious physical illness, serious illness or sudden death of a family member, can lead to depression, with widowhood being the most closely related stressor to depression. People with poor economic status and low social class are also susceptible to the disease. Individuals should be alerted to the onset of depression if a major negative life event has occurred. Susan Nolen-Hoeksema’s study of children followed for 5 years found that the pessimistic explanatory style of personality traits (attributing success to the environment and failure to oneself) was an important predictor of depression onset. Pre-morbid personalities of depression include conscientiousness, enthusiasm, meticulousness, responsibility, stubbornness, inability to accommodate, and inability to improvise.