 FDA has accepted atypical antipsychotics of olanzapine and aripiprazole as the adjuvant medications for refractory major depression. But there is still no trial about atypical antipsychotics combined with antidepressant of SSRI used in fresh major depressive patients. This project aims to compare the efficacy and tolerability of sertraline with or without low-dosed aripiprazole added in fresh major depression. 