Major depressive disorder (MDD) is one of the most common psychiatric disorders, with high recurrence rate, suicide rate and disability rate. It's reported that the global burden caused by MDD will be up to the second rank among all the disease burdens by 2020. China is also confronted with the daunting challenges against MDD. It's assessed that the monthly incidence of MDD is 6.1%, non-hospitalizing rate reaches up to 92% and the non-treatment rate is approximate 95%. However, to date, the pathogenesis of MDD is obscure and the current therapies don't work well. Therefore, it's urgent and critical to elucidate the pathogenesis of MDD, to develop early diagnostic criteria and effective intervention in MDD. Considering the diversity of weights on genetic factor and environmental factor in MDD, in this project, the investigators aim firstly to explore the effect of "genetic-environmental interaction"on the pathogeny of MDD for classifying MDD into "genetic type", "environmental type" and "others" based on a case-control study. We next conduct the neurobiological, neurocognitive and psycho-behavioral assessments among MDD, schizophrenia and healthy groups to screen the salient endophenotypes for establishing the diagnostic models of MDD . The investigators further analyse the changes of these indicators after 8 weeks'medication to select the potential predictors for therapeutic evaluations and interventional options in MDD patients. Finally, the investigators continue a 2-year follow-up study to test and verify the predictors of prognosis in MDD patients.