The starch-acrylamide-diallyl dimethyl ammonium chloride graft copolymer (St-AMDADMAC copolymer) was prepared firstly. Then the synthesized St-AM-DADMAC copolymer was analyzed by FTIR and SEM. Finally the synthesized St-AM-DADMAC copolymers were applied in making packaging paper, the first pass retention and the mechanical properties of the made packaging paper were determined. The FTIR of St-AM-DADMAC copolymer indicated that AM and DADMAC can be grafted in the chain of starch. The SEM of starch and St-AM-DADMAC copolymer indicated that the surface of starch had been changed obviously by grafting copolymerization. The first pass retention increased with the increase of degree of cationic of St- AM-DADMAC copolymer. When the dosage of St-AM-DADMAC copolymer was about 1% and the degree of cationic of St-AM-DADMAC copolymer was about 25.96%, the mechanical properties of the packaging paper were improved best.