OBJECTIVE： To study improvement effect and mechanism of Shuangshen yin on liver function and the degree of liver fibrosis in liver fibrosis model rats. METHODS： Healthy SD rats were collected and given 40％ CCl4 olive oil solution intraperitoneally for consecutive 7 weeks to induce liver fibrosis model. 47 model rats were randomly divided into model group， positive control group and Shuangshen yin low-dose， medium-dose and high-dose groups， with 9， 9， 9， 10， 10 rats respectively； another 10 healthy SD rats were included in normal group. From the next week after model induction， model group and normal group were given water intragastrically； positive control group [colchicines 0.2 mg/（kg·d）] and Shuangshenyin groups [Shuangshen yin water decoction 3， 6， 12 g/（kg·d）， by crude drug] were given corresponding medicines respectively for consecutive 28 d. The serum levels of liver function indicators （ALT， AST， TBIL， ALB， GLB） were determined by Rye’s analysis method. The serum levels of liver fibrosis indexes （HA， LN， Ⅲ-PC， Ⅳ-C） were determined by ELISA. The pathological changes of liver tissues were observed by HE staining and VG staining. The levels of SOD， MDA and HYP in liver tissues were determined by spectrophotometry. The expression of α-SMA was detected by immunohistochemistry. RESULTS： Compared with normal group， the serum levels of ALT， AST， TBIL， HA， LN， PC-Ⅲ and Ⅳ-C in model group were increased significantly， and the level of ALB was decreased significantly （P＜0.05）. There were some pathological phenomena such as vacuolar degeneration and fibrous tissue proliferation in rat liver. The levels of SOD in liver tissue were decreased significantly， while the levels of MDA and HYP were increased significantly （P＜0.05）. A large number of positive staining granules of α-SMA protein were observed in liver tissue， and the expression level of α-SMA protein was significantly increased （P＜0.05）. Comparison of model group， the serum levels of ALT， AST and liver fibrosis indexes were significantly decreased and ALB level was significantly increased in Shuangshen yin groups， while the TBIL levels in Shuangshen yin medium-dose， high-dose groups were significantly decreased （P＜0.05）； the phenomena of hepatocyte degeneration and fibrosis tissue proliferation were significantly improved； the levels of SOD in liver tissue were significantly increased， and the levels of MDA and HYP were significantly decreased （P＜0.05）； the positive staining of α-SMA protein decreased significantly， and the expression level of α-SMA protein was decreased significantly （P＜0.05）. CONCLUSIONS： Shuangshen yin has protective and anti-fibrotic effects on liver in rats with hepatic fibrosis， the mechanism of which may be associated with enhancing antioxidant capacity， down-regulating the expression of α-SMA， inhibiting the activation of hepatic stellate cells， reducing extracellular matrix synthesis so as to reverse liver fibrosis.