The invention discloses a preparation method of a copper-stibium-selenium thin film for a solar cell light absorption layer. The method comprises the following steps of weighing a compound raw material containing a copper source, a stibium source and a selenium source according to the molar ratio of a copper-stibium-selenium compound for prefabricating the copper-stibium-selenium thin film, adding the compound raw material to a binary mixed solvent, stirring and completely dissolving; adding an alcohol organic solvent, stirring evenly and coating an electrode substrate, drying, carrying out repeated painting and drying, and depositing a precursor thin film on the electrode substrate; and putting the precursor thin film into an inert gas or a selenium source-containing atmosphere and heating the precursor thin film to obtain the copper-stibium-selenium thin film. According to the preparation method, use of a toxic and harmful solvent is avoided, the deposition ratios of copper, stibium and selenium elements can be accurately grasped, the prepared thin film is good in crystallization property, uniformity and stability, large in thickness, high in photoelectric conversion efficiency, low in film-forming temperature, simple in process, easy to operate, good in repeatability and low in cost, a large-area and high-quality thin film is easy to prepare, and the preparation method has a very wide application prospect in a solar cell industry.