The patent design provides one method for preparing photoelectricity thin film used in solar cell. It belongs to the field of photoelectric film preparation technology. The SnSe2 nanosheet was prepared from the solid powders of SnCl22H2O and SeO2. The hydrazine hydrate, NaOH and ammonia are used as reducing agents and assistant agent respectively in the patent. It includes the steps of reacting, heating, washing, drying to prepared Tin diselenide. The obtained SnSe2 with high purity has good dispersivity, and regular and uniform shape. The method has a wide application prospect because of safety process and the pollution-free and manageability aided solution.