The invention relates to a flexible stainless steel substrate copper-indium-gallium-selenium film battery which has a combined structure comprising a stainless steel foil substrate and a multi-layer film, wherein the multi-layer film comprises a bottom electrode, an absorption layer, a buffer layer, an intrinsic ZnO layer, an aluminum-doped ZnO layer and a gate electrode which are superimposed together in order. A preparation method of the flexible stainless steel substrate copper-indium-gallium-selenium film battery comprises the following steps of: depositing a double-layer Mo back electrode on the stainless steel substrate by adopting a magnetron sputtering method; preparing a copper-indium-gallium-selenium absorption layer by adopting a three-step co-evaporation method; preparing a CdS buffer layer by adopting a chemical water bath method; preparing the intrinsic ZnO layer and the aluminum-doped ZnO layer by adopting the magnetron sputtering method; and preparing a Ni/Al gate electrode by adopting a thermal evaporation method. The flexible stainless steel substrate copper-indium-gallium-selenium film battery and the preparation method thereof disclosed by the invention have the advantages that: a copper-indium-gallium-selenium film with a preferential growth structure (220) is prepared by using the method, so that the problem that the bonding force between a blocking layer and other contact layers is poor is solved, and the preparation process is simplified; and under the condition of AM1.5 illumination, the battery efficiency of the film solar battery is more than 11.0 percent, and the film solar battery plays an important promotion role when applied to the field of solar batteries.