In this study, chitosan was modified by acrylamide and acrylonitrile when NaHSO3-K2S2O8 as initiator under N2. Chitosan-acrylamide-acrylonitrile ternary graft copolymer was synthesized on the use of radical polymerization mechanism. The optimal experimental conditions for the preparation are obtained by orthogonal experiments: the reaction temperature 65°C, the reaction time 6.5h, the concentration of NaHSO3 3mmol/L, the concentration of K2S2O8 4.5mmol/L, and the ratio of m(chitosan):m(acrylamide):m(acrylonitrile) was 1:6:4. Under such conditions, the average graft ratio and the graft efficiency could achieve 852.455% and 85.260% respectively. Chitosan and chitosan-acrylamide-acrylonitrile ternary graft copolymer were then characterized by means of XRD and SEM, and the graft mechanism was explored preliminary as well. The results showed that chitosan was modified successfully by graft polymerization, and the surface property and the strength of the product were also improved obviously.