The cationic polyacrylamide flocculant P(AM-MAPTAC) was prepared by polymerizing acrylamide(AM) and methacrylamide propyl trimethyl ammonium chloride (MAPTAC) under UV irradiation conditions. Determination the structural features and thermal stability of P(AM-MAPTAC) by IR and TG/DSC. The Response Surface Method was used to obtain the optimum preparation conditions:pH 4.75, initiator mass fraction 0.07%, EDTA-2Na mass fraction 0.20%, MATPAC/AM molar ratio 0.33, illumination time 60min.Under optimal conditions, the intrinsic viscosity of P(AM-MAPTAC) reached 14.72dL/g, under this condition, P(AM-MAPTAC) showed the best effect of sludge dewatering, FCMC 70%, SRF 6.94×10¹² m/kg, tubidity 9.70 NTU.