Abstract: Using ultrasound-assisted extraction,the optimum extraction process of polysaccharides from Onchidium struma was optimized by response surface method combined with single factor experiment. Three methods of deproteinization(Sevage reagent method,enzymatic method and enzymatic-sevage method)were compared to inquiry the best deproteinization conditions. UV,IR,monosaccharide composition and molecular weight of polysaccharides were analyzed and inhibition activities of α-glucosidase were investigated. Results showed that,when the extraction temperature was 90℃,the extraction time was 76 min,and the ultrasonic power was 753 W,the polysaccharide yield was 10.19%. The best deproteinization effect was obtained by enzymatic-sevage method,protein removal rate was 98.52%,polysaccharide retention rate was 96.50%. Polysaccharides existed the characteristic absorption peaks and the trend of ultraviolet spectra. Monosaccharides consisted of mannose,rhamnose,glucuronic acid,galacturonic acid,glucose and fucose with 1.34×10⁶ Da average molecular weight. At the concentration of 50 μg/mL,the inhibition rate of α-glucosidase was 81.9%,slightly higher than that of acarbose. This study provides a theoretical basis for the high-value utilization of Onchidium struma polysaccharides.