Cationic polyacrylamide (P(AM-DAC)) is synthesized by aqueous copolymerization using composite initiator system consists of redox initiator and organic initiator A. The optimum conditions used are as follows: the mass fraction of the redox initiator is 0.15‰, the mass fraction of the organic initiator A is 0.50‰, the gross mass fraction of monomer is 30%, the cationic degree is 40%, and the amount of solubilizer B is 0.20‰. Under these conditions, the molecular weight of the product got is 1.2×107, the dissolving time is 3 h. The structure is proved by IR analysis. DTA-TGA analysis shows that P(AM-DAC) can not be decomposed at room temperature. The results of concentrated sludge dewatering test show that good sludge dewatering results can be achieved using self-made P(AM-DAC) with 40%~80% cationic degree, the transmittance of filtrate is higher than 92%, and the water content ratio of filter cake is lower than 68%. The best sludge dewatering result can be achieved by using the self-made P(AM-DAC) with molecular weight 1.2×107 , cationic degree 40%, the optimum dosage 1.47 kg/t dry sludge, and the transmittance of filtrate is 96.90％, the water ratio of filter cake is 64.50％. The sludge dewatering performance is better than flocculants used in domestic sewage treatment works.