Inclusion Criteria:  Male or female aged 18 to 65 years subjects from outpatients; Subjects currently meet the Diagnostic and Statistical Manual of Manual Disorders, fifth Edition(DSM-5) criteria for MDD with either single or recurrent episodes (296.2/296.3) without psychotic characteristics; Subjects has a total score of the Montgomery- Åsberg Depression Scale (MADRS) ≥26 points at screening; Subjects has a clinical Global Impression -severity illness (CGI-S) score≥4 points at screening  Exclusion Criteria:  Allergic or known to be allergic to venlafaxine and desvenlafaxine; Subjects with MDD who were not responsive to the previous venlafaxine treatment with sufficient amount and duration and to at least two different mechanisms of action antidepressants with adequate amount and duration in the past; There is a clear suicide attempt or behavior and score of the 10th item (suicidal ideation) in MADRS scale is 4 points or greater; Pregnant or lactating women,women who have a planned pregnancy in the near future; Subjects meet the diagnostic criteria for other psychotic disorders(except for MDD) in DSM-5, such as Schizophrenia Spectrum and Other Psychotic Disorders, Bipolar and Related Disorders, Obsessive-Compulsive and related Disorders, post-traumatic stress disorder, separation disorders, anorexia nervosa or bulimia and personality disorder; Subjects who meet the diagnostic criteria for substance or alcohol abuse (excluding nicotine or caffeine) 6 months prior to the screening; MDD secondary to other mental illnesses or physical illnesses; Those with a history of seizures (except for convulsions caused by febrile seizures in children).