The cationic starch with low degree of substitution was half-dry prepared from corn starch,CTA and NaOH.The preparation of cationic starch were optimized by response surface methodology(RSM),based on a Box-Behnken design.The effects of the reaction temperature,the reaction time,the ratio of NaOH and CTA,the water content were explored.Regression coefficient and variance analysis showed that the regression model fits the actual process well.The optimum technology conditions were confirmed as followings: the reaction temperature 64.40℃,the reaction time 6.58 h,the ratio of NaOH and CTA 2.12,the water content 25.28%,the degree of substitution was 0.0519.