Paper industry is one of the major environmental pollution industries in china, pulp and paper industry wastewater discharge amount is from 10% to 12% of the national total wastewater discharge amount. Cationic starch graft copolymer was prepared in laboratory and used to treat papermaking wastewater. The effects of its cationic degree, dosage, flocculation temperature, flocculation time and the combination with alum on papermaking wastewater treatment were investigated. It was found that the best flocculation in the treatment of papermaking wastewater is achieved when cationic degree of cationic starch graft copolymer is 27.38%, adding amount is 15mL, flocculation temperature is 50°C and the mass ratio of alum to cationic starch graft copolymer is 2: 1. The flocculation of composite flocculant made up with alum to cationic starch graft copolymer to papermaking wastewater is much better than only cationic starch graft copolymer is used.