Abstract: Objective To study the effect on Yi Qi Yang Yin Fang on reversing multidrug resistance of the human lung adenocarcinoma A₅₄₉DDP cell line.Methods Serum pharmacology was applied, the mechanism of Yi Qi Yang Yin Fang on reversing multidrug resistance was inquired by MTT or FCM.Results Yi Qi Yang Yin Fang can inhance the inhibition of DDP to A₅₄₉DDP line cell, and it shows significant synergies and efficiency;the combination of Yi Qi Yang Yin Fang and DDP can make cell cycle of the human lung adenocarcinoma A₅₄₉DDP line cell block, and induce apoptosis of the human lung adenocarcinoma A₅₄₉/DDP line cell.Conclusion Reversing apoptosis-resistance to chemotherapy drug of multidrug-resistance tumor line cell maybe one of the mechanism of Yi Qi Yang Yin Fang on reversing multidrug resistance.