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.　Experimental　parameters　covered　the　molten　salt　and　water　flow　fluxes　of　283.1–305.9　kg/m2s,　38.7–64.4　kg/m2s,　the　water　pressures　of　15–19　MPa,　the　water　and　molten　salt　inlet　temperature　of　260　°C/　360–560　°C,　and　heat　fluxes　of　43–266　kW/m2,　respectively.　The　heat　transfer　performance　of　molten　salt　and　water　in　the　single-phase　and　subcooled　boiling　regions　were　analysed　with　respect　to　molten　salt　flow　fluxes　and　inlet　temperature,　water　flow　fluxes　and　pressure.　Based　on　the　experimental　data,　the　heat　transfer　characteristics　of　molten　salt　to　subcooled　water　was　compared　to　the　classical　Grimson　correlation,　with　a　maximum　deviation　of　−20%.　Finally,　the　fitting　correlation　of　the　thermal　performance　of　molten　salt　to　the　subcooled　boiling　water　was　presented,　the　fitting　values　demonstrated　good　consistency　with　the　experimental　data,　with　a　maximum　deviation　of　–10%.　©　2020