Objective:To optimize the condition of anthrone-sulfuric acid method to determine the polysaccharide isolated from Bletilla striata by central composite design/response surface methodology.Methods:Dextron T20 was a standard substance

independent variables were the ratio of the polysaccharide and anthrone-sulfuric acid

the time of color hydrolysis and the cooling time at room temperature

dependent variable was the UV absorption

nonlinear mathematic models were used to estimate the relationship between independent and dependent variables.Response surface methodology was used to optimize be condition of determination.Results:The optimum conditions of determination:the volume ratio of the polysaccharide and anthrone-sulfuric acid is 1:2;the time of color hydrolysis is 8.00 min;the cooling time at room temperature is 15.00min.On this condition

there was favorable correlation between the absorption of Dextron T20 and polysaccharide of Bletilla striata.Conclusions: Central composite design/response surface methodology can be used to evaluate the feasibility and applicable conditions of the anthrone-sulfuric acid method to determine the polysaccharide isolated from Bletilla striata using Dextron T20 as a standard substance.