Abstract: Based on the single factor experiment,response surface analysis was used to optimize the extraction process of polysaccharide from Hemerocallis citrina by ultrasonic synergy rectangular pulse high voltage electric field. Meanwhile,the scavenging abilities of polysaccharide from Hemerocallis citrina to ·O₂^-,·OH,DPPH· were determined.Results showed that the best process conditions of ultrasonic synergy rectangular pulse high voltage electric field were as follows:Extraction time 30 min,extraction temperature 59 ℃,ultrasound power 700 W,electrical voltage 14 kV,the yield of Hemerocallis citrina polysaccharide was 10.03%,which was close to the predicted yield,indicating the extraction process was feasible. The results of in vitro antioxidant activity showed that Hemerocallis citrina polysaccharide had certain scavenging ability on ·O₂^-,·OH,DPPH·,and positively related to the concentration of crude polysaccharide of Hemerocallis citrina,when the concentration of Hemerocallis citrina polysaccharide was 1 mg/mL,scavenging rates on three free radicals could reach 66.93%,70.61%,49.28% respectively. This study provided a new extraction technology for polysaccharides from Hemerocallis citrina.