Cationic polyacrylamide was prepared by inverse emulsion copolymerization using acrylamide (AM) and methacryloyloxyethyltrimethyl ammonium chloride (DMC) as monomers. The influences of the factors, such as emulsifier concentration, initiator concentration, monomer concentration and cationic degree, on the molecular weight and particle size of polymer were investigated. The effects of pH and temperature of waste water and polymer dosage on flocculating results were studied in flocculating experiment. The obtained optimum conditions were emulsifier weight fraction 7.3%, initiator weight fraction 0.02%, monomer weight fraction 45% and cationic degree 25%. Under the above conditions,the molecular weight and particle size of polymer were 339.2 104 and smaller than 70 nm respectively. And the flocculating rate and dewatering rate were 62.2% and 82% respectively under the conditions of wastewater pH 5—6 and polymer dosage 0.057%.