Response surface methodology was used to optimize the microwave- assisted extraction of flavonoids from cold pressed cake in Zanthoxylum armatum DC. Prodr， and the antioxidant activity in vitro of flavonoids were analyzed. The results showed that the optimum extraction process of flavonoids were： microwave power 506 W, microwave treatment time 256 seconds, ethanol concentration 75%, ratio of liquid to material 501. Under this condition, extraction ratio of flavonoids was 0.40%±0.04% ( in terms of rutin). The reducing power, the hydroxyl free radicals, DPPH free radicals, scavenging capacity of flavonoid extracts were increased gradually with the increasing of the mass concentration, and the reducing power of 0.05 mg/mL flavonoids from cold pressed cake was equal with 0.03 mg/mL V_C; the half inhibition concentration of hydroxyl free radical scavenging rate of flavonoids from cold pressed cake and V_C were 0.074, 0.053 mg/mL while the half inhibition concentration of DPPH free radical scavenging rate were 0.024, 0.016 mg/mL. The flavonoids from cold pressed cake had a certain antioxidant activity in vitro, and had the value of developing into natural antioxidants.