Abstract: The total-flavonoid in Stellera chamaejasme L.was extracted by ultrasonic technology and its content was determined by colorimetry,and the cleanup rate of the polyphenolic extract towards superoxide anion radical and hydroxyl radical also was determined with control of ascorbic acid.The result showed that the content of total-flavonoid were 24.30%,and the flavonoids extract from S.chamaejsme L.had remarkable function of removing superoxide anion radical and hydroxyl radical in vitro and it was stronger than VC.The conclusion could be made that it is a promising natural antioxidant for the exploitation and development.