In this paper,first,a concentric circular tube model for the shell-tube heat exchanger with molten-salt phase change materials（PCMs） is established.Then,the liquid fraction and the total melting time,which are affected by the thermal-physical parameters of the molten salt fluid and the PCMs as well as by the inlet velocity and the flow direction of the inner tube,are analyzed with Fluent,by taking into consideration the natural convection in the PCMs region.Finally,some experiments are carried out on a test platform of molten-salt heat transfer.The results show that the total melting time nearly decreases by 16.2% considering the natural convection in the PCMs region,and that the simulated temperature of PCMs at the shell side varies with time,which has a tendency similar to that of the experimental results.Thus,it comes to the conclusion that,when the temperature of the specific measu-ring point in the PCMs region exceeds the melting point of PCMs and rises to the tube inlet temperature,the corresponding time cost can be used as the criterion of melting ending of PCMs.