SOF2,　SO2F2,　SO2　and　HF　are　common　decomposition　products　of　local　overheating　fault　in　SF6　insulated　power　equipment,　but　the　formation　mechanism　and　reaction　pathways　of　these　are　still　not　clear.　It　has　brought　great　difficulties　to　detect　local　overheating　fault　based　on　decomposed　components　analysis　(DCA)　method.　In　this　paper,　the　formation　mechanism　and　reaction　pathways　of　SOF2,　SO2F2,　SO2　and　HF　under　local　overheating　fault　are　studied　by　quantum　chemistry　theory.　The　quantum　chemistry　calculations　were　carried　out　by　Gaussian　software.　The　structural　optimizations,　vibrational　frequency　calculations　and　zero-point　energy　calculations　of　the　reactants,　products,　intermediates　and　transition　states　were　carried　out　by　DFT-B3LYP/6-311++G(d,p).　The　single　point　energies　are　obtained　by　CCSD(T)/aug-cc-PVTZ.　Based　on　the　above　information,　the　formation　mechanism　and　reaction　pathways　of　SOF2,　SO2F2,　SO2　and　HF　under　local　overheating　fault　are　accurately　analyzed,　and　the　influence　of　trace　H2O　and　O2　on　SOF2,　SO2F2,　SO2　and　HF　are　reasonably　explained.　The　research　results　can　provide　theoretical　guidance　for　the　condition　monitoring　and　fault　diagnosis　of　SF6　insulated　power　equipment.　©　2019　IEEE.