In this paper, plasma gradient etching of alumina/epoxy resin surface is realized by combining plasma surface etching method and gradient modification method. Scanning electron microscope (SEM), surface profiler, X-ray photoelectron spectroscopy (XPS), high resistance meter, flashover voltage and surface potential measurement system were used to compare the surface morphology, chemical elements and electrical parameters of untreated, uniform plasma etching and gradient plasma etching samples, and the mechanism of improving the surface flashover performance by gradient plasma etching was studied. The results show that plasma surface etching can improve the surface roughness of epoxy resin, increase the surface conductivity, shallow the trap energy level and increase the surface flashover voltage. The enhancement of flashover voltage by plasma gradient etching is better than that by plasma uniform etching, and the maximum increase is 26.5% compared with the untreated sample. The analysis shows that the electric field distribution of the needle-needle electrodes can be separated into the high field intensity region (near the triple junction) and the low field intensity region (between the electrodes). Speeding up the surface charge dissipation rate in the high field intensity region and properly controlling the surface charge migration rate in the low field intensity region can improve the overall surface flashover performance of the sample to the greatest extent.