Abstract: The weak interaction in the interface layer between nanosilica and epoxy resin limits the improvement of the electrical performances for the composite. Consequently, the CF₄/N₂ plasma cooperated with coupling agent was adopted to modify nano-SiO₂ filler and to change the interfacial characteristics of composites, and nanosilica/epoxy resin composites with different mass fractions were prepared. The chemical compositions, surface morphology, flashover voltage and breakdown field strengths of the composites were tested. The experimental results indicate that the main existing mode of the fluorine element is CF₂ functional group. After plasma fluorination, the averge particle size of nanofillers is reduced by 27.9%, and the agglomeration of the nanosilica is effectively inhibited. Compared with pure epoxy resin, the flashover voltage for the composite with 3% fluorinated SiO₂ is increased by 10.58%. The maximum breakdown field strength and the volume resistivity of the fluorination modified nanosilica/epoxy resin are 33.7 kV/mm and 2.5×10¹⁵ Ω·cm, respectively, which are higher than those of unmodified sample by 11.6% and 34.61%. Plasma processing can introduce the fluorine element on the surface of SiO₂ particles. The migration inside the composites is inhibited and the electrical properties of the composite are improved significantly.