The　accumulated　charges　on　the　insulator　surface　become　a　key　factor　to　incur　surface　flashover.　The　charge　accumulation　process　is　closely　related　to　the　surface　condition.　This　research　investigates　the　effects　of　surface　roughness　on　surface　charge　accumulation　behavior　and　surface　flashover　performance　of　alumina-filled　epoxy　resin　spacers　in　SF6/N-2　mixtures　under　DC　voltage.　The　insulator　is　prepared　with　only　half　surface　subjected　to　rough　treatment.　The　accumulated　charges　are　distributed　in　two　regions.　Considerable　homo-charges　are　located　near　the　high　voltage　(HV)　electrode　and　few　hetero-charges　are　near　the　grounded　(GND)　electrode　(region　I).　These　charges　are　injected　by　electrodes.　The　bipolar　charges　between　HV　and　GND　electrodes　(region　II)　originate　from　gas　ionization.　Surface　rough　treatment　can　suppress　surface　charge　accumulation　and　improve　surface　insulation　strength.　When　increasing　surface　roughness,　surface　charge　declines　first　slowly　(stage　I)　and　then　rapidly　(stage　II),　which　coincides　with　the　two　stages　of　surface　flashover　voltage　increment.　Surface　charge　declination　at　stage　I　is　mainly　due　to　the　increase　in　surface　conductivity,　while　at　stage　II,　the　introduced　deep　traps　also　play　a　role.　Surface　flashover　voltage　increment　at　stage　I　is　mainly　due　to　the　extended　creepage　distance,　while　at　stage　II,　the　declination　of　surface　charge　also　plays　a　role.　Besides,　the　block　of　electron　avalanche　development　by　the　roughed　surface　is　also　responsible　for　the　increase　in　surface　flashover　voltage　at　these　two　stages.　Published　by　AIP　Publishing.