Abstract: In a previous work, a two-stage microstructure was proposed and demonstrated to be able to sharply improve surface flashover voltage of polymer insulators in vacuum. In this paper, the two-stage microstructure was separated into two sub-structures, i.e., surface micro-groove structure and surface micro-hole structure, to study the voltage improvement mechanism in the two-stage microstructure. Through the synthesis of a composite material, laser treatment and acid corrosion, the two-stage microstructure was prepared as well as the two sub-structures. Flashover test of the insulators with the three kinds of surface structures showed that construction of micro grooves and micro holes on the surface of insulators could both enhance the surface flashover strength and their combination could further enhance the flashover strength. The results indicate that through proper combination of different kinds of surface structures multiple suppression of the flashover could be achieved and the surface flashover voltage could be further improved.