Abstract: A thermodynamic model of the phosphorus distribution ratio(LP) of CaO-MgO-FeO-Fe₂O₃-SiO₂ steelmaking slags was developed based on the ion and molecule coexistence theory(IMCT) of slags and verified by experimental data. The predicted phosphorus distribution ratio of CaO-MgO-FeO-Fe₂O₃-SiO₂ steelmaking slags in a temperature range of 1823 to 1873 K by the developed IMCT-LPmodel is more accurate than the measured as well as the predicted phosphorus distribution by other phosphorus distribution models. The developed IMCT-LPmodel can calculate not only the total phosphorus distribution of the slags but also the respective phosphorus distribution of ion pairs(Ca²⁺ + O^2-),(Mg²⁺ + O^2-),and(Fe²⁺+ O^2-) in the slags.