A method improves yield of an upgraded metallurgical-grade (UMG) silicon purification process. In the UMG silicon purification process, in a reaction chamber, purification is performed on a silicon melt therein by one, all or a plurality of the following techniques in the same apparatus at the same time. The techniques includes a crucible ratio approach, the addition of water-soluble substances, the control of power, the control of vacuum pressure, the upward venting of exhaust, isolation by high-pressure gas jet, and carbon removal by sandblasting, thereby reducing oxygen, carbon and other impurities in the silicon melt, meeting a high-purity silicon standard of solar cells, increasing yield while maintaining low cost, and avoiding EMF reduction over time. An exhaust venting device for the purification process allows exhaust to be vented from the top of the reactor chamber, thereby avoiding backflow of exhaust into the silicon melt and erosion of the reactor.