Considering the limitations of experimental studies on thermophysical properties of cryogenic phase change materials (PCMs), a highly accurate approach to predict the solid-liquid equilibrium (SLE) of PCMs is proposed, in which the method of referenced state by a hypothetic path is used in the fugacity of PCMs in the solid phase and the Soave-Redlich-Kwong (SRK)-UNIFAC model is applied in the liquid phase. Based on this method, the thermophysical properties of cryogenic composite PCMs including eutectic composition, eutectic temperature, and eutectic enthalpy are predicted with a minor deviation. Taking the liquid natural gas (LNG) air separation unit as an example, the established simulating method with high accuracy to predict the thermophysical properties of the PCMs is adopted for material selection and design for a cold storage unit in this project with high efficiency.