Abstract: Based on single-factor experiments,response surface methodology(RSM)was employed to optimize the water extraction process of crude Atrina pectinata polysaccharides(CAPPS). The constitute and antioxidant activity of CAPPS obtained by the optimized process were analyzed. The optimal extraction conditions were found to be extraction duration of 215 min at 94 ℃ with a water/material ratio of 34:1 (mL/g). The yield of crude polysaccharides under the optimized conditions was 18.37%. The contents of polysaccharide,protein,uronic acid and sulfate were 94.39%,2.8%,0.63% and 0.08% respectively. Structure and monosaccharide composition of crude polysaccharide were determined by infrared multispectral scanner and chromatographic analysis. And the results showed that crude CAPPS was made of glucose. The results indicated that CAPPS has the eliminating activity on superoxide anion free radicals and hydroxyl radical,as well as metal-chelating ability,and IC₅₀(the half-inhibitory concentration)values were 0.599 mg/mL,1.01 mg/mL and 0.29 mg/mL respectively. The results in the current study would provide a theoretic basis for future studies on activity and development of functional products with CAPPS.