Abstract: To investigate the efficient method of total flavonoids from Syringa oblata leaves, this paper firstly used cellulase-assisted ultrasound method to extract flavonoids from four Syringa oblata leaves. The effects of cellulase dosage, pH, ultrasound time, ultrasound power, liquid-material ratio, temperature and ethanol volume fraction on the extraction rate of total flavonoids from Syringa pubescens Turcz. leaves were analyzed by single-factor experiments, and the best extraction process was obtained by applying response surface methodology optimization. The scavenging ability of Syringa oblata leaves flavonoids on DPPH and OH radicals was also examined in vitro as an antioxidant. The results showed that, the optimum extraction process was enzyme addition 2%, pH5.5, sonication time 40 min, sonication power 400 W, ethanol volume fraction 63%, temperature 56 ℃, liquid to material ratio 30:1 (mL/g), and under these conditions, the Syringa oblata flavonoids content was 32.21±0.16 mg/g, which was in proximity to the predicted value of 32.57 mg/g from the regression model. The results of antioxidant activity showed that the scavenging ability of the four Syringa oblata leaf flavonoids on DPPH was Syringa pubescens Turcz.>Syringa reticulata var. mamds huricq.>Syringa oblata var. affinis lingdelsh.>Syringa oblata Linal. The scavenging ability on OH was Syringa pubescens Turcz.>Syringa reticulata var. mamds huricq.> Syringa oblata Linal.>Syringa oblata var. affinis lingdelsh. The cellulase-assisted ultrasonication method can efficiently extract flavonoids from Syringa oblata leaves, and the flavonoids of Syringa oblata leaves have good antioxidant properties and have certain potential for development.