Chitosan-AM-DMDAAC(Acrylamide, AM; diallyl dimethyl ammonium chloride, DMDAAC) graft copolymer was synthesized by γ-ray irradiation using chitosan, AM and DMDAAC. The effect of reaction conditions on graft copolymer were studied, including absorbed dose, monomer AM and DMDAAC weight ratio, chitosan and total monomers weight ratio, as well as reactant concentration. The results showed that grafting ratio, cationic degree and grafting ratio of DMDAAC increased with the absorbed dose, however, the graft efficiency changed little, and the optimal absorbed dose was 4 kGy. The values of grafting ratio, grafting efficiency and cationic degree were 210.9%, 96.1% and 26.9% respectively; the grafting ratio and the grafting efficiency increased with the AM and DMDAAC weight ratio; when AM and DMDAAC weight ratio is 7:3, they reached maximum values that were 182.6% and 98.8% respectively; the grafting ratio, cationic degree and grafting ratio of DMDAAC increased with the decreasing of chitosan and total monomers weight ratios, and grafting result was the best when chitosan and total monomers weight ratio was 3:8. The values of grafting ratio, grafting efficiency and cationic degree were 182.5%, 94.9% and 25.5% respectively; the grafting ratio, cationic degree and grafting ratio of DMDAAC increased first and then decreased with the decreasing of reactant concentrations, and the optimum amount of acetic acid was 100 mL.Cited