Abstract: The present invention pertains to a method of producing solar-grade polysilicon ingot conducive to reduce the energy consumption and cost and have high yield of casting ingot without complicating equipments. It includes melting and heating raw materials into raw water; mixing the slag removal with the water for eliminating metal impurities; conducting some water vapor for obviating B-atomic and generating pure water, thereafter heated from 1500°-1700° C.; advance heating the crucible and graphite mold in the temperature range of 1000°-1400° C., further pouring the pure water therein and having water temperature from 1450°-1600° C.; adjusting the temperature of the crucible and mold from 1400°-1430° C., thence to the range of 1000°-1200° C. for concentrating the solid/liquid property and impurities of the water on central of the mold; reducing the temperature of the crucible range of 1000°-1200° C. to 200°-400° C., thus finishing an integral polysilicon ingot.