The novel cationic flocculant of CMCTS-g-CPAM was synthesized by polymerizing carboxymethyl chitosan (CMCTS), acrylamide (AM) and methacryloyloxyethyl trimethyl ammonium chloride (DMC) under ultraviolet (UV) radiation. The response surface method was adopted to obtain the optimum preparation conditions:illumination time 2 h, initiator mass fraction 0.04%, pH=8. FT-IR and ¹H-NMR of the graft copolymer indicated that AM, DMC and CMCTS have been successfully aggregated. Additionally, it can be verified by sludge dewatering test that it has good sludge dewatering performance:SRF decreased from 9.10×10¹³ m/kg to 1.96×10¹³ m/kg, and FCMC decreased from 90.15% to 79.28%,at the flocculant dosage and pH of 30 mg/L and 10, respectively. Sludge dewatering effect and economic benefits of CMCTS-g-CPAM are significantly precede to commercially available CPAM. Simultaneously, the research provides a reference for the flocculation treatment in the field of sludge dewatering and the application of chitosan modification in sludge dewatering.