The invention discloses a method and a device for preparing 6N polycrystalline silicon by vacuum microwave refining of industrial silicon, wherein the method comprises the following steps: flowing industrial silicon melt into a primary oxidation refining furnace, introducing mixed gas I, adding SiO2 powder to perform primary oxidation refining, flowing into a secondary oxidation refining furnace, vacuumizing the system, and introducing mixed gas II; then adding SiO2 powder to perform secondary oxidation refining, enabling the mixture to flow into a directional solidification crucible to be subjected to primary vacuum evaporation and directional solidification refining, and heating the materials to be subjected to secondary vacuum evaporation refining; cooling and taking out the silicon ingot, removing the head, tail and edge portions, and crushing and screening the product; then feeding the product into a reactor and vacuumizing the equipment, feeding argon and mixed gas III, and carrying out microwave plasma vacuum evaporation and oxidizing volatilization refining to prepare polycrystalline silicon of which the purity is not less than 6N, the content of metal impurities such as boron, phosphorus, iron and the like is less than 0.1 ppm, the resistivity is about 2.5 ohm.cm. According to the invention, the quality requirement of the polycrystalline silicon solar cell material is met, and the high-quality and high-efficiency monocrystalline silicon solar cell material can be obtained through subsequent casting or single crystal drawing.