It　is　an　important　way　by　detecting　SF6　decomposition　products　to　evaluate　the　insulation　condition　of　SF6　insulated　power　equipment.　In　this　paper,　N-3&Ni　doped　555-777graphene　(N-3&Ni-graphene)　is　proposed　as　a　new　gas　sensor　to　detect　the　characteristic　components　of　SF6　decomposition　products:　H2S,　SO2,　SOF2　and　SO2F2.　In　order　to　get　insights　into　the　gas　sensing　mechanism,　the　geometry　structures,　electron　structures　and　conductivity　are　analyzed　by　simulation　method　based　on　density　functional　theory.　The　calculation　results　show　that　N-3&Ni　dopant　can　improve　the　conductivity　and　surface　activity　of　555-777graphene.　Specifically,　H2S　and　SO2　absorbing　on　N-3&Ni-graphene　surface　will　increase　the　conductivity　obviously,　while　the　other　two　kinds　of　gas　molecules　will　decrease　the　conductivity.　The　sensitivity　of　H2S　is　greater　than　SO2　according　to　the　changed　value　of　energy　gap.　It　is　also　indicated　that　N-3&Ni-graphene　can　absorb　the　above　four　characteristic　components　stably　with　high　adsorption　energies,　complex　orbital　hybridizations　and　multi-level　charge　transfer.　This　work　will　provide　some　theoretical　guidance　to　develop　a　novel　gas　sensor　to　evaluate　the　insulation　condition　of　SF6　insulated　equipment.