Abstract: The effect of CaO content on the liquidus of a CaO-Al₂O₃-22% MgO-1% SiO₂-2% FeO system and the influence of CaF₂ and B₂O₃ contents on the liquid content of the slag at 1700℃ were calculated using Phase Diagram and Equilib module in thermodynamic software FactSage. The starting and ending melting temperatures of the slag obtained from production were measured by differential thermal analysis. When the CaO content in the slag is controlled at 25% approximately for FeV alloy production by the electrical thermite method, the melting property of the slag is good. The effect of CaF₂ on the melting point depression of the slag is better than that of B₂O₃. Meanwhile, these two fluxes are not suitable to be used together when the mass ratio of Al₂O₃/MgO is high in the slag. Considering industrial application and environmental protection, the best addition of CaF₂ in the slag is 2% to 5%.