Abstract: The incidence of adolescent depression continuously increasing recent years, while this problem lacking of effective therapeutic intervention. The classic formula Sinisan (SNS) is known for its function to regulate liver-qi stagnation and treat depression. Our previous study has confirmed its antidepressant effect on adolescent depression, but its neural mechanism still remains to be fully clarified. The study aimed to observe the effect of SNS and its neural mechanism of dorsal raphe nucleus (DRN) region on early life stress induced depression rat model during different stages of adolescence. The adolescent depression rat model was built by maternal separation during postnatal day (PND) 1 to 21. The stages of adolescence were divided into early-, mid- and late-adolescence, accordingly to PND 21-34, PND 34-46 and PND 46-59. The depression-like behaviors were tested during different stages of adolescence by sucrose preference test and forced swimming test. Immunofluorescence double-labeling staining was used to detect changes in neuronal activation in the DRN, transmission electron microscopy was employed to observe the ultrastructure of synapses, and related proteins were assayed. For the inhibitor experiment, catheter implantation surgery was performed from PND 22-30, inhibitor drug intervention on PND 30-47, and behavior tests on PND 43-47. The expression of PSD-95 was measured via Western blot. The results of behavior tests suggest that MS could induce depression-like behaviors in mid- & late-adolescence, and SNS may ameliorate adolescent depression through modulating AMPA receptor for activating BDNF/AKT/mTOR signaling pathway. SNS dose-dependently improved the activation of 5-HT neurons in the DRN, improved the expression of AMPA receptors and SYN/PSD-95 protein, repaired synaptic plasticity. Increased GluA1 protein expression level and decreased NMDAR2B protein level were observed after SNS treatment. Correlation analysis demonstrated the GluA1 and NMDAR2B protein levels were related to depression-like behaviors in mid- and late-adolescence. Treatment combined with SNS and AMPAR inhibitor further confirmed that SNS effectively suppressed the loss of AMPAR in the DRN caused by maternal separation. Therefore, the efficacy of SNS on MS-induced adolescence depression may involve the regulation of AMPAR expression and neural activity in the DRN, recovers synaptic plasticity, and activates BDNF/AKT/mTOR signaling pathway. These results provide reliable experimental evidence for the TCM clinical application of preventing and treating depression during mid- & late-adolescence induced by stress in early life.