Abstract: The low degree of substitution carboxyl methyl amphoteric starch was synthesized by wet reaction process with cassava starch，3-chloro-2-hydroxypropyltrimethylammonium chloride（CHPTMA）and sodium chloroacetate as material，50% ethanol aqueous solution as medium，and NaOH as catalyst. By single factor experiment，experiment studied on the effect on the dosage of NaOH、CHPTMA、sodium chloroacetate 、temperature and time to reaction. The optimum conditions were followings：The mole ratio of sodium hydroxide to sodium chloroacetate and CHPTMA was 2.22，temperature was 40℃，time was 4 hours，the dosage of sodium chloroacetate was 2.5%，and the dosage of CHPTMA was 3.5%.The sample′s cationic degree of substitution was 0.028，anionic degree of substitution was 0.011 .The samples had distinct effect on strengthening in papermaking experiment.