Inclusion Criteria:  Inclusion criteria for healthy subjects:  Healthy subjects should provide a physical examination report within the last year, which could confirm they had not major systemic diseases, such as cardiovascular, respiratory, digestive, urinary, hematological, endocrine and neurological disease; 18 ≤ age ≤ 60 years, both gender; Subjects have clear consciousness and could communicate with others normally; Subjects could understand the full study protocol and written informed consent is provided by themselves. Note: Subjects who meet the above four items will be included.  Inclusion criteria for MDD patients:  Meeting the above diagnostic criteria for MDD; PHQ-9 score of 5 to 14, HAMD score of 21 to 35, and a diagnosis of mild or moderate depression by a specialist; (3)18 ≤ age ≤ 60 years, both gender;  (4) Patients have clear consciousness and could communicate with others normally; (5) Patients could understand the full study protocol and written informed consent is provided by themselves; (6) Those who did not use other therapies other than the basic treatment and this experimental therapy. The basic treatment refers to basic antidepressant medications under the supervision of a specialist. The basic antidepressant medications are Selective Serotonin Reuptake Inhibitors, Serotonin-Norepinephrine Reuptake Inhibitors, Norepinephrine-Dopamine Reuptake Inhibitors, Tricyclic antidepressants, Monoamine Oxidase Inhibitors. Note: Subjects who meet the above six items will be included.  Exclusion Criteria:  Exclusion criteria for healthy subjects:  Subjects suﬀering from mental illness, severe depression, alcohol dependence or a history of drug abuse; Subjects in pregnancy, lactation or menstrual period; Subjects have a fever; Subjects have visible skin damage or scars in the face; Subjects participating in other trials. Note: Subjects who meet any of the above will be excluded.  Exclusion criteria for MDD patients:  Patients with bipolar disorder; Patients with schizophrenia or other mental disorders; Patients with severe medical diseases, tumors or diseases of the central nervous system; Patients suﬀering from severe depressive episode with psychotic symptoms; Suicidal patients; Patients with seasonal depression; Patients with organic depression; Patients with alcohol or drug addicts; Patients using other therapies; Patients in pregnancy or lactation; Patients suffering from cognitive dysfunction, aphasia or other diseases that cannot cooperate with treatment; Patients with pacemakers; Patients who are not suitable for EA. Note: Subjects who meet any of the above will be excluded.