In order to accelerate the dissipation of the surface charge and improve the flashover voltage of insulator, we propose the plasma fluorination modification technology. Changing the surface modification time, the surface physical, chemical, and dielectric properties of epoxy resin sample with the same formula as insulator was test before and after modification. The results show that as a method of both physical and chemical surface modification, plasma modification can introduce hydrophilic groups to the surface of the sample and change its wettability. With the increase of modification time, the surface roughness of the sample increases at first and then decreases. At the same time, the plasma modification can introduce fluorine to the surface of the material, shallow the surface traps, improve the surface conductivity, and reduce the accumulation of surface charge. Under the selected parameters, the surface flashover voltage increases to the maximum after modification for 9 minutes, and the Weibull distribution calculation shows that the increase rate is about 37.17%. After plasma surface modification for too long, the material structure is damaged, the surface traps become deeper, the surface conductivity and surface flashover voltage decrease.