A　comprehensive　understanding　of　heat　transfer　to　supercritical　fluids　is　essential　to　improve　the　thermal　efficiency　of　some　advanced　thermal　systems.　However,　the　mechanism　remains　unclear　that　how　the　heat　transfer　is　affected　by　local　temperature,　especially　the　near-wall　temperature.　In　this　study,　heat　transfer　experiments　of　supercritical　water　are　conducted　in　a　horizontal　tube.　Five　local　water　temperatures　from　the　near-wall　region　to　the　core　in　a　cross-section　are　measured　to　clarify　the　heat　transfer　process　with　the　operating　pressure　of　23.5–26.5　MPa,　mass　flux　of　200–400　kg·m–2　s–1,　and　heat　flux　of　50–180　kW·m–2.　The　tube　length　and　inner　diameter　are　6000　mm　and　26　mm,　respectively.　The　results　show　that　the　heat　transfer　is　suppressed　and　the　enthalpy　increase　is　no　longer　linear　before　the　pseudo-critical　point.　Heat　transfer　is　dominated　by　the　relative　magnitude　of　buoyancy　and　inertia　force,　which　are　affected　by　heat　flux　and　mass　flux,　respectively.　Moreover,　the　heat　transfer　process　is　divided　into　four　parts,　and　the　heat　transfer　deterioration　occurs　at　the　end　of　part　II　and　restores　in　part　III.　Finally,　a　new　correlation　which　is　suitable　for　supercritical　heat　transfer　in　horizontal　tubes　with　large　diameters　is　developed　based　on　the　present　experimental　data.　©　2022