Abstract: The factors on pulsed vacuum flashover of epoxy composite filled with micro-scale Al2O3·3H2O particles are studied. The effects of coupling agent, dispersion method, curing agent, and surface roughness on the flashover properties are investigated respectively. Compared with the amine curing agent, the casting epoxy resin cured by the acid anhydride has higher flashover voltage. The epoxy composite matrix dispersed by the high shear force has better disperse effect compared with that dispersed by the ultrasonic dispersion method. Epoxy composite filled with micro-scale particles treated by coupling agent has higher flashover voltage than that without coupling agent treatment. After surface polishing, the flashover voltage of the epoxy sample becomes higher.