Surface　charge　accumulation　on　insulator　surface　can　have　great　influence　on　surface　flashover　performance.　An　experimental　system　is　established　to　investigate　surface　charge　accumulation　and　decay　characteristics　of　Al2O3-filled　epoxy　resin　insulators　in　0.1　MPa　SF6　under　DC　voltages.　Surface　potential　is　recorded　by　a　Kelvin　vibrating　probe　connected　to　an　electrostatic　voltmeter.　By　pre-depositing　charges　on　insulator　surface,　the　influence　of　surface　charges　on　surface　flashover　performance　is　studied.　The　results　reveal　that　surface　charge　distribution　appearance　is　the　combined　effect　of　electrode　injection,　back　discharge　and　gas　ionization.　Surface　charge　distribution　has　obvious　polarity　effect.　It　is　concentrated　near　the　HV　electrode　under　positive　voltages　and　dispersed　under　negative　voltages.　The　difference　in　positive　and　negative　surface　flashover　voltage　is　attributed　to　the　difference　in　surface　charge　distribution　under　DC　voltages　of　different　polarities.　Surface　charge　decay　contains　two　stages,　which　satisfies　the　law　of　double　exponential　function.　At　first　stage,　surface　charge　decays　fast,　which　corresponds　to　charges　escaping　from　shallower　traps.　While　it　decays　slowly　at　the　second　stage,　which　corresponds　to　charge　escaping　from　deeper　traps.　Surface　charge　decay　process　is　dominated　by　surface　conductivity　mechanism.　The　pre-deposited　charges　on　insulation　surface　have　great　influence　on　surface　flashover　performance.　The　deposited　positive　charges　can　increase　positive　flashover　voltage　but　decrease　negative　flashover　voltage.