The　correlation　between　the　thermal　transport　properties　and　microstructure　features　of　amorphous　coatings　is　crucial　for　reliable　thermal　insulation　applications.　In　this　work,　an　Fe48Cr15Mo14C15B6Y2　amorphous　coating　prepared　by　high-velocity　oxygen-fuel　spraying　(HVOF)　was　employed　to　reveal　this　relationship　under　long-term　heating.　From　the　combined　effects　of　the　amorphous　phase　and　unique　coating　structure,　the　proposed　coating　exhibits　an　extremely　low　thermal　conductivity　of　1.92　W/(m∙K),　granting　a　significant　potential　for　being　as　metal-based　thermal　barrier　coatings.　Isothermal　annealing　experiments　below　the　glass　transition　temperature　demonstrate　that　the　thermal　insulation　property　can　maintain　stability　with　prolonged　annealing　time,　despite　a　slight　degradation　relative　to　the　as-sprayed　coating　which　is　ascribed　to　structural　relaxation.　Although　nearly　full　crystallization　can　be　slowly　induced　by　annealing　at　the　critical　temperature　of　600　°C,　the　thermal　conductivity　displays　a　distinct　two-stage　variation　with　annealing　time,　which　is　primarily　attributed　to　the　sluggish　sintering　of　the　coating　structure.　Moreover,　grain　growth　and　rapid　structural　sintering　result　in　a　drastic　degradation　of　thermal　insulation　in　the　early　stage　of　annealing　at　850　°C,　whereas　grain　growth　upon　prolonged　annealing　governs　further　variation　of　thermal　conductivity.　The　results　of　this　study　not　only　provide　important　insights　into　the　degeneration　mechanism　of　thermal　insulation　of　Fe-based　amorphous　coating,　but　also　present　an　inspiration　for　exploring　the　degeneration　mechanism　of　the　most　metallic　coatings　serving　at　high　temperatures.　©　2023　Elsevier　B.V.