The invention discloses a flexible-substrate iron silicide (beta-FeSi2) thin-film solar battery and a preparation method thereof, and relates to a structural design of a polycrystalline beta-FeSi2 thin-film solar battery device and a preparation method of a thin-film semiconductor material. The flexible-substrate iron silicide (beta-FeSi2) thin-film solar battery is characterized in that a flexible metal foil is used as a substrate material (1), a bottom electrode is metal molybdenum (Mo) film (2), an n-p node is formed by an N-type polycrystalline thin film beta-FeSi2 (4), a weak N-type polycrystalline thin film beta-FeSi2 (5) and a P-type polycrystalline thin film beta-FeSi2 (6); and a transparent conducting layer is made of aluminium zinc oxide (ZnO: Al) (7). The flexible-substrate iron silicide (beta-FeSi2) thin-film solar battery is characterized in that pn nodes of the solar battery are made of betal-FeSi2 polycrystalline thin film material. The preparation method comprises the step of preparing the bottom electrode (2), a transition layer (3), the N-type thin film layer (4), the weak N-type thin film layer (5) and the P-type thin film layer (6), the transparent conducting layer (7) and an upper electrode metal film (8). The flexible-substrate iron silicide (beta-FeSi2) thin-film solar battery and the preparation method of the flexible-substrate iron silicide (beta-FeSi2) thin-film solar battery have the advantages that the materials of all layers of the battery can be obtained by adopting magnetron sputtering deposition under the vacuum environment, the structure is simple, the weight is light, the bendability is achieved, the cost performance is high, the cost of the raw materials of the battery is low, the preparation method is simple and pollution-free, large-area and large-scale production of battery products is easily carried out by adopting a roll-to-roll continuous mode, and the application field of the battery is wide.