In　this　study,　an　experiment　was　conducted　to　obtain　the　heat　flux　and　heat　transfer　coefficient　of　a　mixed　molten　salt　(60%　NaNO3,　40%　KNO3)　and　water　at　subcritical　pressure　in　a　tube　in　tube　heat　exchanger.　The　control　variable　method　was　used　in　this　study.　The　experimental　parameters　included　the　molten　salt　and　water　mass　fluxes　of　38.7–54.1　kg/m2s　and　212.8–259.6　kg/m2s,　respectively,　water　pressure　of　15–19　MPa,　water　and　molten　salt　inlet　temperatures　of　200–400　°C　and　440–500　°C,　respectively,　and　heat　flux　of　12–160　kW/m2.　The　heat　transfer　performances　of　the　molten　salt　and　water　in　the　subcooled,　subcooled　boiling,　saturated　boiling,　dryout　and　superheated　regions　were　analysed　with　respect　to　the　molten　salt　and　water　mass　flow　rate,　inlet　salt　temperature,　water　pressure,　and　inlet　water　temperature.　The　fitting　correlation　of　the　thermal　performance　of　molten　salt　to　the　subcooled　boiling　or　vapor-liquid　two-phase　flow　was　presented;　the　fitting　values　demonstrated　good　consistency　with　the　experimental　data,　with　a　maximum　deviation　of　–6%　and　+8%.　©　2020