Abstract:In this paper，the extraction process of ultrasound in polyphenol and its antioxidation activity from onion were studied.The extraction condition were optimzed by single-factor and response surface experiments，the best extraction process of polyphenol as follows：the ultrasonic power was 320 W，the ultrasonic time was 0.8 h，the solid-liquid ratio was 1 ∶45（g/mL），and the ethanol concentration was 75%.Under these conditions，the yield of polyphenol from onion was 12.77 mg/g.The result showed that the polyphenol from onion had a strong scavenging effect on DPPH·，hydroxyl radical and superoxide anion radical at the concentration range of 0.05 mg/mL-0.3 mg/mL，indicating that onion polyphenols had good antioxidant activity in vitro.