Abstract: In order to improve surface flashover performances of epoxy composites and investigate the effect of surface trap on surface flashover, in this work, four kinds of epoxy/TiO2 nanocomposites were prepared, and these samples were treated by electron beam irradiation under 30 keV for 5 min and 10 min. Surface conductivity was tested by three-electrode measurement system, surface trap characteristics were analyzed by the surface potential decay system, and DC surface flashover voltages were conducted in a vacuum. The results indicate that proper addition of nanoparticles or electron beam irradiation treatment can effectively reduce surface conductivity, improve surface deep trap level and density, and improve surface flashover voltage. The surface flashover voltage of 2% epoxy/TiO2 nanocomposites via electron beam irradiation for 10 min exhibits a 27.4% improvement compare to that of pristine epoxy resin without electron beam irradiation. Appropriate addition of nanoparticles can alter the energy level and barrier distributions in interfacial region of nanoparticles, while a large number of side groups, end groups, and free radicals in the epoxy molecular chain are generated by electron beam irradiation, both treatments can improve the surface deep trap level and density. As surface deep trap level increases, secondary electron emission becomes difficult, surface charge transport process is suppressed, the surface conductivity decreases, and surface flashover voltage increases. Therefore, electron beam irradiation improves surface flashover characteristics of epoxy nanocomposites by tailoring surface deep trap characteristics.