A method for improving yield of an upgraded metallurgical-grade (UMG) silicon purification process is disclosed. In the UMG silicon (UMGSi) 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, including: 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 purification processes is also disclosed, which 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.