In　oxyfuel　combustion,　CO2-H2O　gas　is　highly　corrosive　to　the　furnace　tubes　materials　in　power　plants.　Sulphur　is　a　general　impurity　in　oxyfuel　combustion,　and　its　presence　in　ash　deposit　has　altered　the　high　temperature　corrosion　of　Fe-Cr　alloys.　This　study　concentrates　on　the　fabrication　of　a　FeCoCrNi　high-entropy　alloy　(HEA)　coating　on　a　T91　steel　using　Selective　Laser　Melting　(SLM).　Microstructural　analysis　reveals　an　excellent　metallurgical　bond　between　the　coating　and　the　matrix.　The　coating　exhibit　slightly　higher　microhardness　than　the　matrix,　and　the　fine-grain　strengthening　can　enhance　the　microhardness　of　the　heat-affected　zone　beneath　coating.　The　coating＇s　excellent　corrosion　resistance　is　verified　through　electrochemical　experiments,　and　the　impacts　of　sulphur　on　the　high-temperature　corrosion　behaviour　of　Fe-9Cr　alloy　and　the　HEA-coated　T91　are　further　studied　using　specimens　deposited　in　FeS2-bearing　ash.　The　Fe-9Cr　alloy　experiences　breakaway　oxidation　in　sulphur-free　ash,　but　the　presence　of　FeS2　in　the　ash　delays　the　growth　of　the　internal　oxidation　zone　and　reduced　the　carburizing　effect　beneath　the　iron-rich　oxide　scale.　The　enhanced　high-temperature　oxidation　behaviour　of　the　HEA-coated　T91　is　assigned　to　the　formation　of　a　continuous　protective　Cr2O3　scale,　which　can　be　further　enhanced　by　the　beneficial　effects　of　sulphur　in　the　ash.　Thus,　this　work　provides　a　feasible　HEA　coating　strategy　to　enhance　the　high-temperature　property　of　steel　substrate　under　sulphur-bearing　ash　condition.