Abstract: Using the extraction rate of polysaccharide as index, optimization of the ultrasonic-assisted water extraction and ethyl alcohol precipitation of polysaccharides from Chenopodium album L.(CAPs)was studied. Based on single-factor experiments, five independent factors were selected as affecting factors during extraction with response surface method. The antioxidant activities of CAPs were evaluated by DPPH radical scavenging activity(DPPH), ABTS radical scavenging activity(ABTS), hydroxyl radical scavenging(·OH). The results showed that the optimal conditions of the ultrasonic-assisted water extraction and ethyl alcohol precipitation of CAPs were as follows:the liquid-solid ratio was 30:1, ultrasonic time was 20 min, ultrasonic temperature was 80℃, ultrasonic power was 460 W, concentration of ethyl alcohol was 100%, under these conditions the yield of CAPs was 5.153%. The CAPs had strong scavenging activity against DPPH·, ·OH and ABTS·radical, and the IC₅₀ values were 1.899 mg/mL, 1.973 mg/mL and 2.827 mg/mL, respectively. Accordingly, the CAPs had a certain antioxidant activity and has a potential value of being exploited as functional food.