In this study, the graft copolymerization of acryalmide and acrylonitrile onto chitosan with K2S2O8-NaHSO3 initiator under N2 interaction is studied and the mechanism is discussed. Compared to the chitosan graft of acrylamide or acrylonitrile, the graft yield and graft efficiency of ternary polymerization increase significantly. The stability and reproducibility are also improved obviously. To be specific, the reaction time, the reaction temperature, the effect of the amount of materials, the concentration of K2S2O8, and the concentration of NaHSO3 on the graft yield and graft efficiency is investigated respectively. The C=C of acrylamide and the acrylonitrile react respectively with -NH2 and C6-OH of chitosan initiated by SO4-•. The experimental results show that the optimal synthesis conditions are given as follows: the reaction time is 6h, the reaction temperature is 60°C, the ratio of m(chitosan):m(acrylamide):m(acrylonitrile) is 1:7:5, the concentration of K2S2O8 is 4.5mmol/L, and the concentration of NaHSO3 is about 2.6mmol/L. Under such conditions the graft yield and graft efficiency can be up to 839.52% and 70.00%, respectively.