NOVELTY - Preparing polycrystalline silicon thin film comprises selecting experimental materials, a substrate and an evaporation source by selecting e.g. polycrystalline silicone powder and aluminum powder (each of purity more than 99.99%), standard aluminum etching solution and glass as substrate, removing oil from substrate, ultrasonically cleaning and washing substrate in deionized water, drying, performing primary and secondary evaporation precipitation, vacuum evaporating silicon film, evaporating aluminum film, and vacuum annealing at 450-650 degrees C for 2-4 hours at a vacuum degree of 3-5x 10-2 Pa.    USE - The film is useful in vacuum evaporation solar batteries.    ADVANTAGE - The method has simple preparation process, high efficiency and low energy consumption, is suitable for mass production, and produces film with good binding force, high purity, high crystallization rate and high photoelectric conversion efficiency.    DETAILED DESCRIPTION - Preparing polycrystalline silicon thin film comprises: (i) selecting experimental materials, a substrate and an evaporation source by selecting polycrystalline silicone powder and aluminum powder (each of purity more than 99.99%), acetone (analytically pure), anhydrous ethanol (analytically pure), standard aluminum etching solution, glass as a substrate, and graphite (99.7%); (ii) removing oil from substrate; (iii), ultrasonically cleaning substrate; (iv) washing the substrate in deionized water, and drying; (v) performing primary evaporation precipitation, where the amount of polycrystalline powder is 0.2-0.6 g, vacuum degree is 4.5-7.5x 10-3 Pa, the substrate temperature is 300-500 degrees C and the substrate distance is 5-15 cm; (vi) performing secondary evaporation precipitation, where the where the amount of polycrystalline powder is 0.1-0.2 g, vacuum degree is 4.5-7.5x 10-3 Pa, the substrate temperature is 300-500 degrees C and the substrate distance is 5-15 cm; (vii) performing vacuum evaporation for the silicon film; (vii) evaporating aluminum film, where the amount of aluminum powder is 0.1-0.3 g, vacuum degree is 4.5-7.5x 10-3 Pa; the substrate temperature is 400 degrees C, and the substrate distance is 5 cm, and (viii) vacuum annealing at 450-650 degrees C for 2-4 hours at a vacuum degree of 3-5x 10-2 Pa. An INDEPENDENT CLAIM is also included for a polycrystalline silicon thin film, prepared by the above mentioned method and comprises a polycrystalline film and an aluminum layer sequentially arranged from the surface to the substrate, where the film has good surface morphology, uniform grain diameter size, and regularly arranged grains with a film thickness of 5-10 mu m, crystalline ratio of 73.2-89.4%, and theoretical photoelectric conversion efficiency of 8.3-10.5%.