Abstract: The preparation conditions of acetylated Auricularia auricular polysaccharide were optimized by combination design of quadratic regression orthogonal,and the antioxidant activity were studied at the same time.In this experiment,amide was used as solvent,acetic anhydride was used as acetylated reagent and N- Bromo succinimide( NBS) was used as catalyst. Indicators for acetylated degree of substitution,and the reaction time,reaction temperature,acetylated reagents and NBS addition were used for investigation of variable factors and by quadratic regression orthogonal combination design method. The final data was analyzed by SPSS software. The results showed that reagent dosage of acetylated and NBS addition of polysaccharide from Auricularia auricular had a significant effect( p < 0.05) on the acetylated polysaccharide preparation.After equation calculations,the preparation optimal acetylated conditions for Auricularia auricular polysaccharide were as: reaction time 3.5 h,reaction temperature 80.0 ℃,acetylating reagent dosage 32.5 m L,NBS addition was 1.0%.Under the experimental conditions,the acetylating of substitution degree average was 0.55. The results of original polysaccharide and acetylating of infrared spectrum detection showed acetylated Auricularia auricular polysaccharide preparation was prepared. Using the optimal conditions for preparation of acetylated Auricularia auricular polysaccharide,the oxidation resistance research showed that the ability of removal hydroxyl free radicals and remove super oxide anion free radical ability were a little improved,and reducing power was also increased