Abstract: Fluorinated nano-modification of epoxy resin (EP) is an essential means to improve the surface voltage resistance properties of composite insulating materials. In this paper, the graphene nanoplatelets (GNPs) are modified in three different forms, including plasma fluorination, chemical fluorination and plasma-chemical synergistic fluorination. By exploring the influence of different fluorination methods on the fluorine-containing interfacial layers, the mechanism of EP composites' DC surface voltage resistance properties can be revealed. The results show that doping the three fluorinated graphene nanoplatelets improves the surface flashover voltage of EP composites. By further analyzing the surface charge dissipation and trap distribution of EP composites, it is found that different grafting forms of GNPs have different mechanisms for improving the surface voltage resistance properties of EP composites. The formation of effective bond between GNPs and EP matrix can promote the charge transport along GNPs, thus affecting the surface voltage resistance of the EP composites.