Abstract: Water-soluble maleylated chitosan (MHCS) was prepared by acylating chitosan with maleic anhydride. P(MHCS-AM) flocculant was graft copolymerized by MHCS and acrylamide (AM) initiated by UV irradiation. The effects of monomer content, reaction time, acetic acid content, the molar ratio of chitosan and maleic anhy‐ dride on the intrinsic viscosity and grafting efficiency of P(MHCS-AM) were discussed. Infrared spectroscopy, scanning electron microscopy and differential thermal analysis were used to characterize the structure and organi‐ zation of P(MHCS-AM), the preparation and flocculation conditions were optimized. The results show that the optimum preparation conditions of P(MHCS-AM) are monomer mass fraction of 12.5%-17.5%, illumination time of 3-5 h, acetic acid mass fraction of 2%-4%, and the molar ratio of chitosan and maleic anhydride of 1∶2-1∶4, and the maximum intrinsic viscosity and grafting efficiency are 2 368.09 mg/L and 163.7% respectively. The graft copolymerization reaction between MHCS and AM is successful, and there are a large number of porous or convex structures on the surface of MHCS, AM is successfully grafted onto MHCS skeleton, and P(MHCS-AM) is stable at room temperature and not easy to decompose. P(MHCS-AM) flocculation performance is significantly better than that of the commercial available polyacrylamide (PAM), inorganic flocculants polymer ferric sulphate(PFS) and polymeric aluminiumte (PAC). The optimized flocculation conditions of P(MHCS-AM) are dosage of 2-4 mg/L, pH value of 6-9, and the hydraulic condition G of 200s^-1, and the removal rate of turbidity can be up to more than 85%.