Abstract: For the sake of further realizing the characteristic of the EOF slag of Pan-Zhi-Hua Steel Works we have drawn and tested the CaO-SiO₂-V₂O₅, FeO-SiO₂-V₂O₅ and CaO-FeO-V₂O₅ ternary phase diagrams which are based upon six binary phase diagrams, and using these diagrams to explain some specific properties of the vanadium bearing slag. The behaviour of the vanadium bearing slag in smelting process has been discussed. The influence of some common oxides on the property of slag as well as on the saturation of MgO in slag have also been calculated and illustrated.