Abstract: The cationic starch with high degree of substitution(DS=0.4) was synthesized by semi-dry process,and its reaction efficiency was 88.89%.The application test results indicated that when the addition dosage of this cationic starch ranging from(200 mg/L) to 300 mg/L and the pH value of the waste=11,COD removal efficiency of the dye-house wastewater can reach 90% and the color stripping efficiency can reach 78%.