Excess sludge, product of sewage treatment, is increasingly produced. Sludge decontamination is required before sludge disposal, and sludge conditioning is a very important step. Cationic sludge dehydrating agent of CMCTS-g-CPAM was synthesized using Carboxymethyl chitosan (CMCTS), acrylamide (AM) and methacryloyloxyethyltrimethylammonium chloride (DMC) as monomers, azobisisobutylphosphonium hydrochloride (V-50) as an initiator through initiating polymerization by ultraviolet light. The preparation conditions of CMCTS-g-CPAM sludge dehydrating agent were optimized by response surface methodology (RSM) taking the photoinitiator concentration, pH and illumination time as the object of investigation, the intrinsic viscosity of CMCTS-g-CPAM as the response value. The optimal illumination time, photoinitiator concentration, and pH of respectively 2h, 0.04% (volume fraction), and 9 were obtained by response surface analysis. FT-IR and 1H-NMR of the graft copolymer indicated that AM and DMC were successfully grafted to CMCTS. Finally, the synthesized product was applied to sludge dewatering. The experimental results showed that it has good sludge dewatering performance. Sludge specific resistance decreased to 1.96×1013m/kg, and the moisture content of the filter cake decreased to 79.28%,at the flocculant dosage and pH of 30mg/L and 10, respectively.