The polysaccharides were extracted from the white double-flowered Hibiscus by ultrasound- assisted hot water extraction technique. Through single factor experiment and Box-Behnken design, the effect of ultrasonic-assisted hot water extraction on the extraction yield of Flos Hibisci polysaccharides(HPs) was studied by response surface methodology, and the mathematical model between the extraction yield and the extraction factors was established.The results showed that the extraction yield of HPs reached 6.36±0.12% when the ultrasonic time was 20 min, the ultrasonic power was 473 W and the ratio of material to liquid was 1:25 g/mL.In vitro antioxidant test preliminarily confirmed that HPs had strong scavenging capacity for hydroxyl radicals (·OH) and superoxide anions (O2–).