The alloying technology is an important part of steelmaking, which has a significant impact on the formation of non-metallic inclusions in the steel. In the current chapter, the influence of residual elements of Al and Ca in ferrosilicon alloys on non-metallic inclusions in the molten steel was quantitatively evaluated. Inclusions evolve from Al2O3 to MgO·Al2O3 to partially liquid CaO-MgO-Al2O3 without the addition of ferrosilicon alloy. The addition of Ca-containing ferrosilicon into the molten steel effectively modified Al2O3 and MgO·Al2O3 inclusions into liquid CaO-Al2O3 ones in Al-killed steel. The high Al-bearing ferrosilicon alloy significantly increased the Al2O3 content in Al2O3-SiO2-MnO inclusions, which led to the formation of pure Al2O3 inclusions in Si-Mn-killed steels. Addition of SiO2 and Fe2O3 into refining slag and top blowing Ar-O2 mixed gas were proposed to remove Al and Ca impurity elements in ferrosilicon alloys. The motion, dissolution, and diffusion of alloys in the molten steel were also modeled discussed, which provided useful directions for the application and clean production of clean ferroalloys.