The invention discloses a polycrystalline silicon preparation method, which comprises the following steps of: refining silicon liquid in a two-man ladle by the combination of gas blowing, NaCl, KCl and SiO2 slag formers and plasmas to remove boron impurities, wherein oxidizing gases are ionized into plasma gas, the plasma gas is continuously fed into the silicon liquid for 1-3 h from the bottom of the two-man ladle, and reaction is performed in the two-man ladle; after the reaction is completed, carrying out treatment on the obtained product so as to obtain low-phosphorus-boron metal silicon; carrying out crushing, grinding and acid-washing on silicon ingots, washing, and drying; melting silicon powder subjected to acid-washing into silicon liquid through heating, and carrying out heat preservation; placing a graphite plate on the surface of the silicon liquid, enabling the bottoms of the graphite plate and a graphite crucible to be respectively connected with negative and positive poles of an external direct-current voltage, wherein the exerted direct-current voltage is 10-100 V; and after carrying out electrification 2-4 h, in an electrified state, dropping the graphite crucible at a speed of 0.10-0.15 mm/min to leave a heating area, carrying out directional solidification, after the silicon ingots are cooled, taking out the silicon ingots, and cutting off an upper impurity gathering area so as to obtain purified 6N polycrystalline silicon. The method is good in removal effect on impurities such as boron, metals and the like, low in cost, and environment-friendly.