Abstract: The melting performance of an Al₂O₃-CaO-MgO ternary slag system and the effect of added fluxes on the melting point of the slag system were theoretically analyzed by using Equilib and Phase Diagram modules in thermodynamic software FactSage. The melting temperature of the slag system from production was measured. It is found that the melting point of the slag system decreases first and then increases with increasing w(Al₂O₃)/w(CaO) ratio, and it reaches the lowest value when w(MgO) is 4% to 5%. At the w (Al₂O₃)/w(MgO) ratio more than 3 and w(CaO) less than 30%, the melting point decreases with increasing w(CaO). When 2〈w (Al₂O₃)/w(CaO) 〈2.5 and w(MgO) is 15% to 18%, the melting point can decrease about 100℃ with the addition of 2.29% AlCl₃, 4.86% Fe₂O₃ or 4.77% Na₂O in the slag system.