Studies　on　candidate　gases　of　SF6,　the　insulating　and　interrupting　medium　in　electrical　equipment,　have　become　a　hot　topic　in　recent　decades.　C5-perfluorinated　ketone　(C5F10O)　was　reported　as　a　potential　replacement　due　to　its　excellent　insulation　capacity.　However,　the　decomposition　property　of　C5F10O　under　discharge,　which　is　closely　related　to　insulation　deterioration　mechanism,　is　still　unknown.　Although　the　fundamental　decomposition　pathways　of　C5F10O　were　reported　[1],　the　corresponding　rate　constants　are　essential　but　not　computed　yet.　Therefore,　we　calculated　the　rate　constants　of　different　decomposition　reactions　using　transition　state　theory　(TST)　combined　with　density　functional　theory　(DFT).　The　structural　optimizations,　vibrational　frequency　calculations　and　energy　calculations　of　the　species　involved　in　reactions　were　carried　out　with　DFT-(U)B3LYP/6-311G(d,　p)　method.　Detailed　potential　energy　surface　(PES)　was　then　investigated　thoroughly　by　the　same　method.　For　reactions　with　a　transition　state　(TS),　each　stationary　point　on　PES　was　analyzed　by　a　harmonic　vibrational　frequency　analysis　and　characterized　as　a　minimum　(reactants　or　products　with　all　real　frequencies)　or　a　TS　(with　only　one　imaginary　frequency).　Intrinsic　reaction　coordinate　(IRC)　calculations　were　used　to　verify　each　TS.　Then　the　corresponding　rate　constants　were　estimated　by　conventional　transition　state　theory　(CTST).　For　barrierless　reactions,　the　broken　symmetry　guess　were　added　for　optimization　where　the　selected　bond　distance　was　held　constant.　Then　the　rate　constants　and　equilibrium　constants　were　estimated　by　canonical　variational　transition　state　theory　(VTST).　The　results　are　hopefully　to　lay　a　theoretical　basis　in　further　evaluating　and　online-monitoring　the　insulation　condition　of　C5F10O　gas-insulated　electrical　equipment.　©　2018　IEEE.