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Effective control of oxygen impurity in multicrystalline silicon is required for the production of a high-quality crystal. The basic principle and some techniques for reducing oxygen impurity in multicrystalline silicon during the unidirectional solidification process are described in this paper. The oxygen impurity in multicrystalline silicon mainly originates from the silica crucible. To effectively reduce the oxygen impurity, it is essential to reduce the oxygen generation and enhance oxygen evaporation. For reduction of oxygen generation, it is necessary to prevent or weaken any chemical reaction with the crucible, and for the enhancement of oxygen evaporation, it is necessary to control convection direction of the melt and strengthen gas flow above the melt. Global numerical simulation, which includes heat transfer in global furnace, argon gas convection inside furnace, and impurity transport in both melt and gas regions, has been implemented to validate the above methods.