Sarcinochrysis marina Geitler polysaccharide(SMP-0) was degraded by H2O2-Vc solution system. After separation and purification by Sepherose6B, three kinds of relative homogeneous products were obtained (SMP-1、SMP-2、SMP-3). The physicochemical properties of different polysaccharides were analyzed and the antioxidation, hygroscopicity and moisture retention activities were evaluated by determining the total reducing capacity, the scavenging ability of free radicals and moisture retention ratio. The results showed that SMP-0, SMP-1, SMP-2 and SMP-3 were sulfated polysaccharide and consisted of arabinose, D+fructose and glucose, but the molar ratio of each sugar had small difference. The antioxidant abilities were inverse proportion to molecular weight of polysaccharides, and showed dose-dependence. The total reducing ability of SMP-3 was closed to Vitamin C. The maximum scavenging activity of SMP-3 on O2-• and •OH were 94.89% and 88.98%, respectively. The hygroscopicity and moisture retention activity of high molecular weight (MW) polysaccharide was superior to that of low MW fragments. The maximum hygroscopic ratio of SMP-0 was 49.18%, which was 8.7% lower than that of glycerol, but was 27.4% and 35.2% higher than that of hyaluronic acid and chitosan, respectively. The maximum moisture retention ratio of SMP-0 was 77.23%, which was obviously higher than that of glycerol (30.02%), but was appreciably lower than that of hyaluronic acid and chitosan.