The testing of the melting-points and viscosity of BaO-SiO2-CaO-Al2O3(5%)-Na2O(10%)-CaF2(1 0%)six-part slag system is completed. Then the curve charts of the melting-points and viscosity are drawn. Moreover, the mathematical relations between properties andchemical compostion are found out.As a result,the proper range of chemical composition for BaO-contained mould fluxes is therefore presented.