A molecular thermodynamic model based on the theory of melting point depression and the modified double lattice model with the free-volume effect is developed to interpret phase behaviors of solid polymer electrolyte (SPE)/salt systems with various pressures. To account for the free-volume effects, we employ the hole-theory proposed by Kleintjens. Quantitative description according to the proposed model is in good agreement with the experimentally observed transition temperatures for given systems. Our results show that eutectic points move toward higher T-m and lower weight fraction region of salt with increasmg pressure.