Abstract: The study aimed to optimize the cellulase extraction process of polysaccharide from Galla chinensis and study its antioxidant activity in vitro. On the basis of single factor test results, Box-Behnken response surface methodology was used to optimize the extraction process of polysaccharide from Galla chinensis with the amount of enzyme, enzymolysis temperature, liquid-to-material ratio and enzymolysis time as independent variables, and the yield of polysaccharide as response value. DPPH radical and hydroxyl radical scavenging rates were used to investigate the antioxidant activities of polysaccharides from Galla chinensis in vitro. The results showed that the optimal extraction conditions of polysaccharide from Galla chinensis by cellulase were as follows: enzyme dosage was 1.3%, enzymolysis temperature was 49℃, liquid-to-material ratio was 13∶1, enzymolysis time was 1.6 h and enzymolysis pH was 4.8. Under these conditions, the yield of polysaccharide from Galla chinensis was 4.27%, and the theoretical prediction value of regression model was 4.32%, and the error between the two conditions was less than 5%. Polysaccharide from Galla chinensis had strong scavenging effects on DPPH free radical and hydroxyl free radical, with median inhibitory concentrations of 0.785 mg·mL⁻¹, 1.173 mg·mL⁻¹, respectively. Cellulase enzymatic method can significantly improve the yield of polysaccharide from Galla chinensis, the process is simple and feasible, and the polysaccharide obtained from Galla chinensis has antioxidant activity in vitro.