Graft copolymerization of granular allyl starch with carboxyl-containing vinyl monomers using $H_2O_2/Fe^{2+}$ initiator in aqueous dispersion was investigated for enhancing grafting efficiency of the copolymerization. The graft copolymerization was evaluated in terms of grafting efficiency, grafting ratio, and conversion of monomer to polymer. Influences of both allyl etherification of starch and structures of vinyl monomers used on the copolymerization were revealed. Variables such as molar ratio of $Fe^{2+}$ to $H_2O_2$, initiator concentration, monomer concentration, polymerization temperature, and time of the graft copolymerization were also studied. It was found that allyl etherification of starch enhanced the grafting efficiency and grafting ratio evidently. Acrylic acid exhibited the greatest grafting efficiency and ratio for the copolymerization after starch was allyl-etherified. The copolymerization should be carried out under the protection of nitrogen gas at $30-35^{circ}C$ for 3 h by using $H_2O_2/Fe(NH_4)_2(SO_4)_2$ as initiator. Preferred molar ratio of $H_2O_2/Fe(NH_4)_2(SO_4)_2$/anhydroglucose was in a range of 20/1/1000 to 60/3/2000.