Abstract: To optimize the ultrasonic-assisted extraction technology of total flavonoids from Citrus aurantium L. var daidai by response surface method and study its antioxidant activity. Firstly,the effects of ethanol concentration,solid-liquid ratio,extraction temperature and time on the extraction yield of total flavonoids by single factor experiment,then the extraction process was optimized by four-factor and three-level design of surface response analysis,at the same time,the antioxidant activity of flavonoids from Citrus aurantium L. var daidai was studied by assessing the DPPH· and ·OH scavenging activities. Results showed that the optimum process conditions for the extraction total flavonoids were as follows:ethanol concentration 60%,the ratio of liquid to solid 20:1 mL/g,extraction time 35 min,extraction temperature was 60 ℃,the extraction yield of total flavonoids from Citrus aurantium L. var daidai was 2.62% under such conditions,which was highly consistent with the predicted value of 2.66%;and the IC₅₀ values of DPPH· and ·OH scavenging activities were 0.385 and 0.255 mg/mL,respectively. The extraction process optimized by response surface method was stable and feasible,and the total flavonoids from Citrus aurantium L. var daidai had strong antioxidant activity.