Abstract: To develop a new type of heat transfer/storage molten salt material that matches solar thermal power generation technology,KNO₃,NaNO₂,and KNO₂ are selected as research objects.Based on the subregular solution model,thermodynamic theoretical calculation is carried out on the phase diagram of the KNO₃-NaNO₂-KNO₂ ternary system,and the phase diagram of the system is simulated using the phase diagram software FactSage 8.2.The eutectic point of the KNO₃-NaNO₂-KNO₂ system is determined through experimental results,and the heat storage capacity of the preferred molten salt is investigated.The results indicate that the eutectic point data of the ternary molten salt calculated using the subregular solution model has high accuracy.The preferred mixed molten salt has the composition of 42.0%KNO₃-48.5%NaNO₂-9.5%KNO₂ （percentages are mole fractions）,with the melting point of 139.8℃，the melting end point of 146.3℃，the heat of fusion of 71.1 J/g,the decomposition temperature of 652.0℃，and the average liquid specific heat capacity of about 1.48 J/（g·K）.