The invention belongs to the technical field of metallurgical purification, and particularly relates to a polysilicon purification method. The method comprises the following steps: performing alloying smelting on metal and metallurgical silicon to obtain a silicon alloy; adding basic slagging agent into the silicon alloy used as a raw material, slagging, smelting, and purifying; and finally, keeping the temperature of the melt, cooling, and separating according to density difference to obtain high-purity silicon, the slagging agent and the silicon alloy, wherein the slagging agent and the silicon alloy can be recovered and used repeatedly. By adding a small amount of metal element into the metallurgical silicon, the metal element and the silicon can be formed into the alloy melt, thus effectively lowering the smelting temperature in the slagging and purifying process and reducing the crucible loss; in the cooling process, impurities have fractional condensation effect between the silicon and the alloy melt, thus effectively lowering the boron impurity content in the primary silicon and improving the purifying effect; and finally, based on the density difference among the silicon, the alloy and the slagging agent, the three phases are separated, thus obtaining the high-purity polysilicon, ensuring that the silicon alloy and the slagging agent can be used repeatedly, and avoiding the reagent consumption and alloy element loss in the subsequent acid washing and purifying process.