Flavonoids were extracted under ultrasonic assistance from Artemisia Annua L. residue where Artemisinin was extracted, using ethanol as extraction solvent. The optimal ultrasonic-assisted extraction technology was determined by single factor experiment and orthogonalexperiment. Meanwhile，antioxidant activity of flavonoids which were purified to oil and fat was evaluated and compared with that of ascorbic acid and citric acid. Results showed: the optimal ultrasonic-assisted extraction technology of flavonoids in Artemisia Annua L. residue is: ethanol volume fraction about 50% , material-to-liquid ratio of 1∶30 (g：mL), ultrasonic power of 200 W , ultrasonic-assisted extracting time about 40 min and extraction temperature at 55℃. The extraction rate of flavonoids reaches 9.10% with the optimal ultrasonic-assisted extraction technology. The removal efficiency of hydroxyl radical increases along with the increase of the purified flavonoids concentration. The purified flavonoids reveales obvious antioxidant effect on oil and fat, it is superior to not only ascorbic acid but also citric acid on oil , it is somewhat higher than that of citric acid but inferior to ascorbic acid on fat.