Under the action of ultrasonic, the graft copolymer is synthesized by grafting 2, 3- glycidyl trimethyl ammonium chloride onto chitosan with ammonium cerium nitrate as initiator, and the main factors which influences this reaction are selected. The results show the optimum reactive conditions while chitosan: 2, 3- glycidyl trimethyl ammonium chloride is 1:3, pH 7.0, 70°C, the reactive time 3h, and the concentration of initiator 0.5mmol/L. Finally, the product of graft copolymer is analyzed by chemical titration, infrared analysis (IR), differential scanning calorimetry (DSC), elemental analysis, and XRD.