A molecular thermodynamic model based on both the theory of melting point depression and the lattice fluid model is developed to interpret the liquidus curves in the resulting phase diagram and predict the change of liquidus curve and an eutectic point with various pressures. Quantitative description according to the proposed model is in good agreement with the experimentally observed transition temperature of a given system and shows that an eutectic point moves toward higher T m and lower weight fraction of salt with increasing pressure.