Abstract: Based on the single-factor experiment,solid/liquid ratio,ethanol concentration,the ultrasonic extraction time and ultrasonic temperature were used as experimental factors and the yield of flavonoid was used as the response value to optimize the extraction of flavonoids from quinoa chaff by the Box-Behnken experimental principle. The in vitro antioxidant activity of the obtained flavonoids was studied. The results showed that the optimal extraction conditions of flavonoids from quinoa chaff were as follows:56% ethanol,the solid/liquid ratio of 20:1 g/mL the ultrasonic time of 14 min and the ultrasonic temperature of 58℃.Under this condition,the extraction rate of flavonoids was 0.802%. Flavonoids from quinoa chaff had extremely significant antioxidative activity which was directly proportional to the mass concentration of extracted flavonoids. It has a certain DPPH free radical and hydroxyl radical scavenging ability,and its ability is positively correlated with its mass concentration. The results showed that the DPPH and hydroxyl free radical scavenging capacity reached about 64% and 77% at the concentration of 0.5 mg/mL. As a by-product of quinoa,quinoa chaff has certain value for development and utilization.