Depression is mainly characterized by depressed mood, slowed thinking and reduced volitional activity, and in most cases, various physical symptoms are also present. (1) Depressed mood: The basic features are depressed mood, distress and sadness, and lack of interest. Feeling pessimistic and desperate, painful and unbearable, with the feeling that life is like a year and life is worse than death. The inner experience is often described as meaningless and unhappy. The typical person has a depressed mood, with the characteristics of heavy daytime and light nighttime. It often coexists with anxiety. (2) Delayed thinking: the thought association process is inhibited, the reaction is slow, and the self-consciousness of the brain does not turn, which is manifested by the reduction of active speech, the speed of speech is significantly slowed, and the thinking problem is laborious. Slow reaction, need to wait for a long time, under the influence of low mood, low self-esteem, low self-esteem, a sense of uselessness and worthlessness, feeling that living is meaningless, pessimistic and suicidal intentions, self-blame and self-sin, thinking that living becomes a burden, committing a big crime, the emergence of suspicion on the basis of somatic discomfort, thinking that they are suffering from an incurable disease. (3) Decreased volitional activity: active activities are significantly reduced, life is passive, reluctant to participate in the outside world and activities that are usually of interest, and often solitary. The laziness of life develops into silence and immobility, and can reach the level of rigor mortis. The most dangerous is the recurrence of suicidal attempts and behaviors. (4) Somatic symptoms: Most depressed patients have somatic and other biological symptoms, such as palpitations, chest tightness, gastrointestinal discomfort, constipation, loss of appetite and weight loss. Sleep disturbances are prominent, mostly difficulty in falling asleep. (5) Other: depressive episodes can also present with hallucinations, depersonalization, dissociation of reality, obsessive-compulsive and phobic symptoms. Depressive pseudo-dementia can occur due to significant delay in thought association and memory loss, which can easily affect the cognitive function of elderly patients. Mild depression often has complaints of dizziness, headache, weakness and insomnia, and is easily misdiagnosed as neurasthenia. The latter has certain psychosocial factors before the onset of the disease, such as long-term tension, overuse of the brain, etc. The emotions are mainly anxiety and vulnerability, and the main clinical phases are emotional symptoms such as mental fatigue, tension, worry and irritability associated with mental arousal, and symptoms of physiological dysfunction such as muscle tension pain and sleep disorders. The self-knowledge is good, the passivity of symptoms is high, and the desire to seek treatment is high. In contrast, depression is mainly depressed mood, accompanied by slow thinking, low self-esteem, self-crime, desire to die, and biological symptoms (such as light mood around the clock, decreased appetite, libido, etc.), often losing self-awareness, and not actively seeking treatment. Occult depression is an atypical depression, mainly manifested by recurrent or persistent various somatic discomfort and vegetative symptoms, such as headache, dizziness, palpitations, chest tightness, shortness of breath, numbness of the limbs and nausea, vomiting and other symptoms, depressed mood is often masked by physical symptoms, so it is also called depressive isotonic disorder. Patients often do not seek psychiatrists but go to other departments. Somatic examination and ancillary tests are often not positive, and are easily misdiagnosed as neurosis or other somatic diseases. Symptomatic treatment is generally ineffective, and antidepressant treatment is effective.