Abstract: The grafting modification of natural starch was carried out by the use of 60Co-γ irradiation. Cation grafted starch was prepared by three steps: first mix a certain amount of corn starch with DMC’s aqueous solution uniformly, then the resultant product is radiated in the 60Co-γ radiation field, finally it is subjected to drying, crushing, and centrifugal extraction. The effects of reaction medium, monomer ratio, radiation dose and dose rate on the sample were investigated, and the affecting factors were analyzed. The best technical parameters of grafting cations onto the starch were determined: ratio of reaction medium(water), 028 ; monomer ratio, 0.06 ; radiation dose, 6 kGy; and radiation dose rate, 10 Gy / min.