Abstract: Polyphenol from Capsella bursa-pastoris was extracted by ultrasonic-assisted, and the extraction process was optimized by response surface methodology. On the basis of single factor experiment, the response surface experiment with four factors and three levels was used to study the effect of ethanol concentration, extraction time, extraction temperature and solid-liquid ratio on the extraction rate of polyphenols. The results showed that the optimal extraction conditions were ethanol concentration of 48%, extraction time of 27 min, extraction temperature of 57℃ and solid-liquid ratio of 1:33 (g:mL), under these conditions, the experimental result was 28.33 mg/g. Compared to the predictive value (28.35 mg/g), the relative error was 0.07%. Comparing with conventional antioxidant ascorbic acid, polyphenols from Capsella bursa-pastoris extraction in vitro could be better removing hydroxyl free radical (·OH), superoxide anion radical (O₂^-·), nitrite and reduction ability, and IC₅₀ value of extracted Capsella bursa-pastoris polyphenols was (0.17±0.01) mg/mL, (0.08±0.01) mg/mL and (18.9±0.02) μg/mL, respectively. Conclusion:polyphenols obtained in Capsella bursa-pastoris is a natural antioxidant and free radical scavenger.