Epoxy resin filled with micron alumina (micro‐Al2O3/ER) has been widely used in the manufacture of basin insulators for its excellent mechanical and thermal properties. However, charge dissipation properties of micro‐Al2O3/ER are too poor to ensure its surface insulation on strength under long‐term action of a DC electric field. In this paper, the modification method of plasma cohydrothermal fluorination of filler was proposed to improve its surface charge dissipation performance. The surface morphology and the element content of Al2O3 were observed, and the flashover voltage and charge characteristics of different composites were tested. Finally, the trap distribution was calculated by isothermal current attenuation method. Self‐comparison analysis with single‐step modification of plasma treatment shows that the cofluorination method has a high graft rate of fluorine element and an ideal modification effect on surface insulation, with its technical means convenient to be applied in the insulator manufacturing industry.

The surface coating of epoxy resin has been widely used in the composite materials with micron scale fillers, but the related research on the composite coating filled with nanoparticles is still rare. SnO 2 is a common antistatic additive in composite materials, and it is also a semiconductor material, capable of uniform voltage. In this paper, nano-SnO 2 powder was considered as the filler of coating materials. By analyzing the microscopic test results, the flashover voltage, surface charge dissipation, and surface conductivity of the coating sample, the effects of coating treatment and nano-SnO 2 fluorination on the surface insulation properties of epoxy insulators were studied. It is found that the flashover voltage and surface charge dissipation rate of the coating sample can be improved by both coating treatment and fluorination treatment, thus improving the surface insulation performance of epoxy insulators. The modification process and test results have guiding significance for improving the surface insulation performance of epoxy insulators.