This paper describes the grafting of acrylamide onto sweet potato starch initiated by potassium permanganate and the effect of the graft copolymer on seed germination. Two orthogonal experiments were carried out to achieve the best graft and saponification conditions. The best graft conditions are that the quantity of starch, monomer, water and the concentration of catalyst, initiator are 1 g, 7.5 g, 100 mL, 1.54×10^-2 mol/L, 1.5 mmol/L respectively. The best saponification conditions are that the quantity of NaOH, the saponifying temperature, the saponifying time are 26 mL/(g monomer), 100℃, 3 h, respectively. The graft copolymer was used to coat corn seeds. The results showed that the germination rate of coated corn seeds was 10% higher than that of uncoated seeds.