The invention discloses a preparation method for preparing a copper-zinc-tin-sulfide (Cu-Zn-Sn-S) thin film solar cell. The thin film solar cell comprises a soda-lime glass substrate, a metal back electrode molybdenum (Mo) layer, a p-type Cu2ZnSnS4 absorption layer, an n-type Cd1-xZnxS buffer layer, a ZnO window layer, and an Al electrode. The method for preparing the p-type Cu2ZnSnS4 absorption layer comprises the steps of adopting a quaternary compound copper-zinc-tin-sulfur target and conducting the one-step sputtering deposition without any subsequent vulcanization process. The n-type Cd1-xZnxS buffer layer reduces the usage amount of Cd and also reduces the environmental pollution. Meanwhile, the short-wave absorption of the solar cell is improved, and the photoelectric conversion efficiency of the solar cell is increased. The elements of the thin film solar cell are non-toxic, pollution-free and rich in reserve volume. The solar cell is simple in preparation process, high in photoelectric conversion efficiency and low in cost, thus being suitable for industrial production.