The invention discloses a preparation method of 
polycrystalline silicon. According to the method, the twin 
crystal growth control technology is adopted, the ordinary polycrystalline process is optimized, a heat insulation cage is quickly opened, and the opening of the heat insulation cage is adjusted to be 6-8cm; at the initial stage of growth of the 
crystal, the temperature of a heater is adjusted to be 1425-1440 DEG C, the heat insulation cage is slowly lifted, a layer of uniform dendritic 
crystal grows vertically on a 
nucleation source layer along the bottom of a 
crucible, then dendritic crystal is taken as the 
seed crystal, and vertically upward directionally grows to form the 
polycrystalline silicon. The 
polycrystalline silicon prepared by the invention contains a great quantity of twin crystals, as the twin crystals have the advantages that the interfacial energy of the twin crystals is low, the twin crystals are relatively more stable, and the like, and the polycrystalline 
silicon prepared by the method has the 
advantage of few 
dislocation defects, the battery efficiency of the polycrystalline 
silicon is higher than that of the ordinary polycrystalline 
silicon for 0.2-0.4%, the average battery efficiency of a whole silicon 
wafer reaches 17.5%, and the highest efficiency reaches 18.0%.