The invention belongs to the technical field of photocatalysis, environmental protection and inorganic materials and in particular relates to a method for preparing a ZnO/ZnS composite photocatalyst film on a metal sheet. The method comprises the following steps: adding a mixed liquor of quadrol and water (or distilled water or deionized water) into a reaction kettle with a polytetrafluoroethylene lining, than adding thiourea, putting a zinc sheet subjected to ultrasonic cleaning by distilled water and absolute ethyl alcohol into the reaction kettle, carrying out hydrothermal reaction at the temperature of 120-180 DEG C for 6-24 hours, naturally cooling, taking out the zinc sheet, washing the zinc sheet for three times respectively by deionized water and absolute ethyl alcohol, and drying at room temperature to obtain the ZnO/ZnS composite photocatalyst film on the zinc sheet, wherein the volume ratio of the quadrol to water is 1:(1-10), and the concentration of the thiourea in the mixed solution is 0.5-3.0 mol/L. With the adoption of the method, a hydrothermal method is adopted to synthesize the ZnO/ZnS composite photocatalyst film by one step, the synthesis method is simple, the uniformity and the controllability of the film are good, and the method is easy to popularize and is suitable for large scale production.