The invention provides a method for preparing a GIGS solar cell by applying a one-step magnetron sputtering method. According to the invention, soda-lime glass is taken as a substrate, Mo / CIGS / CdS / i-ZnO:Al / Ni:Al target materials are sequentially adopted, and a CIGS solar cell with the film thickness being about 1-2 microns through using direct current sputtering and radio frequency sputtering, wherein the Mo target adopts direct current sputtering, the CIGS / CdS / i-ZnO / ZnO:Al sequentially adopt radio frequency sputtering, and the Ni:Al adopts direct current sputtering. Content control for each element is realized through adjusting various parameters in the sputtering process, and a CIGS solar cell with the conversion efficiency reaching 5.77% at most can be obtained. The magnetron sputteringmethod provided by the invention is different from the traditional quaternary co-evaporation, sputtering and post-selenization method, so that there is no need of using a toxic hydrogen selenide gasto prepare a CIGS absorption layer by applying the post-selenization method, but the absorption layer is directly prepared by adopting the selenium-rich CIGS target material, thereby enabling the production process to be simpler to operate, green, environment-friendly and easy to control. In addition, the commercial production can be enabled to be equivalent to laboratory production in productionefficiency, and the method has wide commercial application prospects.