The invention discloses a ZnO(zinc oxide)/chitosan/kaolin nanometer composite material and a preparation method thereof. The method comprises the following steps: adding the chitosan to a mixed solution of a zinc acetate dihydrate aqueous solution and an acetic acid aqueous solution, then adding a NaOH(sodium hydroxide) solution to the mixture of the chitosan and the mixed solution so as to obtain ZnO/chitosan composite material, and then adding the ZnO/chitosan composite materials to kaolin suspension liquid which is activated to react and obtain the nanometer composite material. The nanometer composite material has the advantages that the crystallinity is good, the purity is high, the material has a higher photocatalysis activity under visible light and a good adsorption capacity, and besides organic immobilization and inorganic immobilization of nanometer ZnO are realized; problems that the separation and the recovery of the nanometer ZnO as a single photocatalyst are difficult and the adsorption capacity is poor are solved to a certain extent, and organic pollutants such as dye in water can be removed by adsorption and photocatalysis degradation, so that the method is suitable for treating waste water; the material can be prepared at atmospheric pressure, the reaction condition is mild, the technology is simple, the preparation process is easy to control, and the material has a favorable application prospect.