The invention relates to a silver-copper-selenium ternary compound dendrite film material and a preparation method thereof. The material is a AgCuSe dendrite film material grown on a silver foil substrate. The preparation method comprises the following steps of: soaking a dendritic Ag2Se nanocrystalline film grown on the silver foil substrate in selenium powder and water suspension and nanometer copper powder and ammonia water suspension in turn, and performing chemical reaction at room temperature to directly convert the dendritic Ag2Se nanocrystalline film on the surface of the silver foil substrate into a high-purity AgCuSe ternary compound dendrite film. The AgCuSe dendrite film material is prepared through appearance duplication of a nanomaterial and in-situ reaction, and the phenomenon that a product prepared by other wet chemical reactions is impure is avoided; the AgCuSe ternary compound prepared by the method has an integral stoichiometric ratio, and a crystal has a three-dimensional dendritic structure; in the method, a target product is obtained through the reaction at room temperature, so that the defects of high energy consumption and complicated processes of a high temperature method, an electrochemical method and the like are overcome; and a surfactant and other additives are not needed, so that industrial production and popularization are facilitated.