OBJECTIVE：To study “Qi-invigorating”effect and its possible mechanism of total saponins of Astragalus membranaceus on rats with Qi-deficiency ，and to provide reference for elucidating the material basis of “Qi-invigorating”effect of A. membranaceus . METHODS ：Forty male Wistar rats were randomly divided into normal group ，model group ，positive control group [Buzhong yiqi pills ，4.5 g/（kg·d）]，A. membranaceus total saponins high-dose and low-dose groups [ 252，28 g/（kg·d），by the amount of total saponins] according to body weight ，with 8 rats in each group. Except for normal group ，the model of Qi-deficiency was made in other groups by the method of “diet disorder+fatigue ”. At the same time ，administration groups were given relevant medicine intragastrically ，and normal group and model group were given constant volume of water，once a day ，for consecutive 21 days. After last administration ，the general situation of rats was observed ；the body weight ，spleen index and thymus index of rats were detected ；weight-bearing swimming time was recorded ；the levels of spleen T lymphocyte subsets CD 3 and CD 4，the levels of ATP and ADP in liver tissue ，serum levels of ALB ，RBC and HBG in blood as well as the serum levels of SOD，MDA，lactate，LDH，CK，IL-2，IL-12 and TNF-α were all detected. RESULTS：Compared with normal group ，body weight，thymus index ，spleen index ，weight-bearing swimming time ，the level of spleen T lymphocyte subsets CD 3，ATP，ADP， ALB，IL-2 and IL- 12 were decreased or shortened significantly in model group （P＜0.05 or P＜0.01）. The levels of MDA ， lactate，CK and TNF-α were increased significantly （P＜ 0.05）. Compared with model group ，body weight ，spleen index，weight-bearing swimming time ，the level of spleen T lymphocyte subsets CD 3 and the levels of ATP ，ADP，ALB， RBC and IL- 2 were increased significantly or prolonged（P＜0.05）；while the levels of MDA ，lactate，CK and TNF-α were decreased significantly in A. membranaceus total saponins high-dose group（P＜0.05 or P＜0.01）.Weight-bearing swimming time ，the levels of ATP ，ADP and IL- 2 in A. membranaceus total saponins low-dose group were increased significantly or prolonged （P＜0.05 or P＜0.01），while the levels of MDA ，lactate，CK and TNF-α were decreased significantly （P＜0.05 or P＜0.01）. Compared with positive control group ，spleen index ，spleen T lymphocyte subsets CD 3，weight-bearing swimming time and ATP level of A. membranaceus total saponins high-dose group were increased significantly or prolonged （P＜0.05 or P＜0.01），while MDA levels of A. membranaceus total saponins high-dose and low-dose groups were decreased significantly （P＜0.05 or P＜0.01）. CONCLUSIONS ：A. membranaceus total saponins can reduce the body ’s accumulation of blood lactic acid ，the activity of CK ，the level of lipid peroxide and regulate immunity to tonify Qi ，delay fatigue and improve exercise ability.