The invention discloses a preparation method of a flexible base material and thin film for vacuum reel-to-reel coating. According to the preparation method, a whole stainless steel reel is taken as the base material, a molybdenum-sodium target material is utilized for preparing a first layer of bottom electrode thin film, a sodium element can enters CIGS (copper indium gallium selenium) thin film layer by virtue of diffusion in a high-temperature CIGS evaporation thin film formation process so as to increase the efficiency of a battery, and a sputtering-coated zinc-magnesium-oxygen thin film layer is taken as a buffer layer to replace a CdS (cadmium sulfide) thin film of a conventional immersion method, so that the whole reel of a CIGS solar cell can be produced; a bottom electrode (MoNa), the buffer layer (ZnMgO) and a transparent conducting thin film (95ITO) layer are plated by utilizing a reel-to-reel sputtering coating machine, and a CIGS absorption layer is prepared by utilizing a reel-to-reel evaporation machine, so that the production of the CIGS cell is finished in a full vacuum process, the large-area uniformity is guaranteed, the production efficiency and yield of the cell are substantially increased, the manpower is substantially reduced, the quality and performance of the thin film are improved, and the preparation method meets the production requirements of CIGS thin film solar cells.