The　Fiber　Reinforced　Plastics　(FRP)　with　vacuum　forming　technology　has　high　structural　strength　and　excellent　insulation　property,　and　is　widely　used　in　EMP　(Electromagnetic　Pulse)　simulation　devices.　In　order　to　improve　the　insulation　performance　of　FRP　and　meet　the　requirements　of　the　supporting　structure　for　insulating　materials　in　MV　(Megavoltage)　EMP　simulation　equipment,　the　effect　of　groove　shape　on　the　insulation　performance　of　FRP　insulators　was　studied.　The　experimental　object　is　the　cylinder　insulators　with　different　grooving　technologies.　The　insulation　environment　is　0.1　MPa　SF6,　and　here　we　use　the　circuit　to　output　the　nanosecond　pulse　with　the　rising　edge　of　approximate　30　ns.　The　result　shows　that　in　SF6,　different　from　the　vacuum　condition,　the　concave　grooves　of　different　shapes　and　sizes　have　no　significant　influence　on　the　flashover　voltage　along　the　surface　of　insulators,　which　indicates　that　the　secondary　electrons　production　on　the　surface　of　insulators　may　not　be　the　main　reason　for　the　flashover　process　along　the　surface　in　SF6.　The　result　also　indicates　that　convex　grooves　can　reduce　the　electric　field　on　the　development　path　of　the　flashover　channel　and　change　the　angle　between　the　development　path　of　the　streamer　and　the　electric　field　on　the　surface　of　the　insulator,　thus　improving　the　withstand　voltage　of　the　insulator.　Besides,　in　the　experiments　of　samples　with　convex　grooves,　the　bulk　breakdown　phenomenon　of　insulator　and　its　convex　grooves　were　observed,　showing　that　there　is　a　competition　between　the　bulk　breakdown　in　the　insulator　and　the　flashover　along　the　surface　of　insulator　whose　phenomenon　may　be　related　to　the　impurities　(bubble　or　dust)　introduced　along　the　glass　fiber　during　the　manufacturing　operation.　©　2020　IEEE.