Abstract: The experiments was conducted to study the influence of acetylated modification on scavenging free radicals, NO-2effect of green tea polysaccharides. Orthogonal experiment was designed to study the optimal conditions of acetylated modification. Acetylated green tea polysaccharides was produced on this optimal conditions, and superoxide anion free radical, hydroxyl free radical and NO-2scavenging effect in vitro were compared before and after modification.Superoxide anion free radical, hydroxyl radical and NO-2scavenging effect experiments with different substitution degree acetylated tea polysaccharide were conducted, and relationship between the different substitution degree and scavenging activities were analyzed.The optimal conditions of acetylated modification were: mass of tea polysaccharide / volume of acetic anhydride 1 ∶ 40, holding time 4h, reaction temperature 30℃, the maximum substitution degree was 0.337 in this experiment, and the maximum increased ratios of superoxide anion free radical, hydroxyl free radical and NO-2scavenging effects were 32.06%, 36.96%, 55.99%. Besides, superoxide anion free radical, hydroxyl radical and NO-2scavenging activities were increased with the increase of substitution degree. The results showed that acetylated modification could improve the effect of free radicals, NO-2scavenging activities of green tea polysaccharides and scavenging activities was related with substitution degree.