Abstract: The ultrasonic-assisted extracting technology of polysaccharides from Kochia Scoparia ( Linn.) Schrad was optimized by response surface methodology. Based on the single factor experiment, a quadratic polynomial regression model and the optimal extraction conditions was established about the dependent variable ( extraction yield of polysaccharide) and independent variables ( liquid-material ratio, ultrasonic power, ultrasonic temperature and ultrasonic time) through a four factors-three levels Box-Benhnken design and response surface methodology. The scavenging effect of polysaccharides on 2, 2-diphenyl-1-picrylhydrazyl ( DPPH) free radical was also studied and comparing with ascorbic acid ( VC) and tertiary butylhydroquinone ( TBHQ) .The results showed that the optimum conditions of ultrasonic-assisted extraction of polysaccharides from Kochia Scoparia ( Linn.) Schrad were as follow: liquid-material ratio 21 m L/g, ultrasonic power 76 W, ultrasonic temperature 72 ℃ and ultrasonic time 24 min and yield of polysaccharide could reach up to 58.45 mg/g, the relative error was 1.15% compared to the predictive value, which indicated the feasible model fitted well with the experimental data. The Kochia Scoparia ( Linn.) Schrad polysaccharides could effectively eliminate the DPPH free radical, indicating that the polysaccharides had a certain antioxidant capacity.The antioxidant capacity followed the order, VC> polysaccharides > TBHQ.