The invention relates to a method for preparing high-purity polysilicon from high-purity metallic silicon. Under the protective atmosphere of high-purity argon, a graphite crucible is taken as an anode, a vertical graphite electrode arranged in the middle of the graphite crucible is taken as a cathode, horizontal grates are staggered and arranged from top to bottom on the outer wall of the graphite electrode, the high-purity metallic silicon in the graphite crucible is heated to 1650-1800 DEG C and generates silicon vapor, the silicon vapor runs up to pass through the grates, and the high-purity polysilicon is collected after cooling treatment. Compared with the traditional purification process, the invention not only greatly reduces the purification technological process, but also has stable process and high efficiency, and reduces the raw material cost for solar batteries, so that obtained high-purify polysilicon has stable purify and good consistency. The production cost of purification equipment is low, no pollution is discharged in the production process, and the environmental protection is good.