Since there were a lot of amino, hydroxyl, and N- acetyl reactive functional groups distributed on the chitosan macromolecule chains. The modification of chitosan as natural green flocculants had received more and more attentions, but the graft copolymer product thereof spectroscopic characterizations were rarely reported. Therefore, the spectroscopic characterization and analysis of the chitosan-based flocculants were of great significance. The chitosan based flocculant CS-P(AM-DMDAAC) was synthesized by photopolymerization method using chitosan (CS), acrylamide (AM), and diallyl dimethyl ammonium chloride (DMDAAC) as the monomers of graft copolymerization. X-ray diffraction (XRD), Ultraviolet spectroscopy (UV), and Infrared (IR) spectroscopy were applied to investigate the structural characteristics of CS-P(AM-DMDAAC). The characteristic of spectrum and the attributions of characteristic absorption peaks of CS, AM, DMDAAC, and CS-P(AM-DMDAAC) were analyzed by the X-ray diffraction (XRD), ultraviolet spectroscopy (UV), and infrared spectroscopy (IR). The effects of degree of deacetylation of chitosan, concentration of chitosan, cationic degree of graft copolymer on X-ray diffraction (XRD), Ultraviolet spectroscopy (UV), and Infrared (IR) spectrum of CS-P (AM-DMDAAC) were systematically investigated. Ultraviolet spectroscopy (UV) and Infrared (IR) spectrum demonstrated that AM and DMDMAAC were successfully grafted onto CS to prepare CS-P (AM-DMDAAC). The increase of chitosan concentration led to weakening spectrum symmetry. X-ray diffraction showed that the crystal structure of chitosan was transformed into amorphous structure by the graft copolymerization. Compared with the amorphous structure, the crystal structure was more easily hydrated, so the graft copolymer product had more excellent solubility.