According to the definition of disordered entropy, we obtain the equation of state (EOS) of liquid metals. Then due to the fact that the fraction of liquid present in the mixed phase region is assumed to be not linear with temperature but linear with volume, the incorrect hypothesis of the fraction of liquid present in Grover model is clarified. The more accurate formula to express the EOS of solid-liquid mixed phase is obtained. The calculations from Grover model show that the solidus, liquidus and melting line do not coincide in the P-T graph as they should be. The modified results are shown to be in good coincidence with the three lines in the P-T graph.