Surface　flashover　properties　of　alumina/epoxy　spacers,　involving　a　surface　charge　accumulation　process,　are　critical　for　the　safe　and　reliable　operation　of　a　high-voltage　direct-current　(HVDC)　gas-insulated　transmission　line　(GIL).　This　study　reports　surface　charging　behavior　and　flashover　performance　of　alumina/epoxy　spacers　with　different　surface　conductivity　graded　coating　(SCGC)　schemes　in　SF6/N2　mixtures　under　DC　stress.　Four　kinds　of　SCGC　schemes,　i.e.　localized　coating　near　high　voltage　(HV-coating),　near　grounded　electrode　(GND-coating),　at　the　middle　of　spacer　surface　(SPM-coating)　and　near　both　high　voltage　and　grounded　electrode　(HV-GND-coating),　are　designed　by　partially　spraying　SiC/epoxy　composites　on　the　spacer　surface.　Surface　charge　distribution　patterns　exhibit　varied　features　with　different　SCGC　schemes.　The　HV-coating　and　GND-coating　schemes　lead　to　aggravated　homo-charge　and　hetero-charge　accumulation　respectively,　whereas　in　the　SPM-coating　scheme　surface　charge　shows　a　multi-tier　distribution　pattern　with　alternating　polarity.　A　transition　of　the　dominant　surface　charge　mechanism　from　bulk　conductivity　to　surface　conductivity　with　increasing　conductivity　on　the　coated　area　is　found.　Flashover　performance　differs　a　lot　with　different　SCGC　schemes:　the　HV-coating　and　HV-GND-coating　schemes　increase　the　flashover　voltage　while　the　SPM-coating　and　GND-coating　schemes　degrade　it.　The　optimal　surface　insulation　strength　is　achieved　in　the　HV-coating　scheme　with　a　coating　width　of　about　10　mm.　The　impact　of　different　SCGC　schemes　on　flashover　performance　is　revealed　based　on　the　electric　field　analysis　by　considering　the　effect　of　surface　charges.　©　2020　IOP　Publishing　Ltd.