The invention relates to a polysilicon recovery technology, and provides a method for preparing solar grade polycrystalline silicon by efficiently recovering a diamond wire cutting silicon powder. Themethod comprises the following steps: firstly, pre-treating the silicon powder waste, then granulating the silicon powder waste by a high energy density heating method, directionally solidifying thegranulated silicon blocks in vacuum, and finally smelting the silicon ingots with electron beams. The laser or arc heating method used has the characteristic of high energy density, so that the ultrafine silicon powder in a certain region can be melted instantaneously and rapidly solidified into silicon blocks having certain volume before severe oxidation. With the high energy density granulationprocess, the yield of silicon is 95%, which significantly improves the filling efficiency of the subsequent smelting process and reduces the cost. Moreover, the vacuum directional solidification of impurities and the electron beam smelting are further combined to remove volatile impurities such as P and O, so that the removal rate of impurities can be improved more effectively, and the solar gradepolycrystalline silicon is finally obtained.