Ultrasonic-assisted ethanol extraction after heating was used to extract polyphenols from corn silk. On the basis of single factor test, the response surface optimization test was carried out on polyphenols by ultrasonic-assisted ethanol extractions, and the antioxidant activity of the extracted polyphenols was studied. The results showed that the optimum extraction conditions were as follows: the ratio of solid to liquid 122 (g/mL), the volume fraction of ethanol 60%, the ultrasonic time 32 min, and the ultrasonic temperature 60 ℃，the extraction rate of the polyphenol from corn silk was (6.49 ± 0.23)%. The scavenging rates of DPPH，hydroxyl and ABTS free radicals by corn silk polyphenols were equivalent to the reduced glutathione, which were detected to be 0.917, 0.809, 0.881 mg /mg, respectively.