Abstract: The synthesis craft of cationic starch flocculation under microwave radiation was studied.Through orthogonal experimenting, the optimal conditions was obtained as follows:the mole ratio of sodium chloride, 2,3-epoxypropyl trimethyl ammonium chloride and starch is 1.4∶1∶2.2, the reaction time under microwave radiation is 1.5 min, and the power of microwave oven is 800 watt.