Study to Explore the Effective Doses and to Assess the Safety and Efficacy of Hypidone Hydrochloride Tablets

Inclusion Criteria: 1. Outpatient or Inpatient, 18-65 years old, male or female 2. Current major depressive disorder diagnosed by DSM-5, single episode(296.21, 296.22, 296.23), or recurrent episode(296.31, 296.32, 296.33) 3. Montgomery-Åsberg Depression Rating Scale (MADRS) total scores in both Screening and Baseline ≥ 26 4. The first item of MADRS in both Screening and Baseline ≥ 3 5. CGI-S in both Screening and Baseline ≥ 4 6. Able to provide written informed consent forms Exclusion Criteria: 1. Subjects accord with other mental disorders diagnosed by DSM-5 2. Subjects who attempted to suicide, or who presently have a high risk of suicide, or with the tenth item (Suicidal ideation) of C-SSRS ≥ 3 3. Baseline total scores compared with the screening period, the reduction rate of MADRS ≥ 25% 4. Subjects with serious or uncontrolled cardiovascular disease, liver disease, kidney disease, blood disease, endocrine disease, respiratory disease 5. Subjects with clinically significant ECG abnormal (Male QTcF ≥ 450 msec, Female QTcF ≥ 470 msec) 6. Treatment with a MAOI within the 2 weeks prior to the first dose of trial medication 7. Practicing 2 different treatment methods of antidepressants as recommended dose of full course (≥6 weeks) 8. Subjects who have had a Vagus Nerve Stimulation (VNS) device implanted, or who have received Modified Electric Convulsive Therapy (MECT) or Transcranial Magnetic Stimulation (TMS) within 3 months of Screening, or who received light treatment, laser treatment, acupuncture and other Chinese medicine treatment, biofeedback treatment within 2 weeks of Screening 9. Subjects with a history of true allergic response to more than 1 class of medications 10. Subjects who participated in a clinical trial within the last 30 days