To improve the vacuum surface flashover performance of insulators, a kind of composite surface structure consisting of micro grooves and molecule self-assembly membrane was proposed and prepared on the surface of alumina vacuum insulators by laser carving, water cleaning and molecule self-assembly. Meanwhile, insulators with only micro grooves or pure molecule membrane were also prepared. The secondary electron emission yield test showed that both the micro groove structure and molecule self-assembly could reduce the secondary electron emission yield of the alumina insulator. Their combination (the composite surface structure) could further reduce the secondary electron emission yield. Correspondingly, the surface flashover voltage test indicated that surface micro groove construction and molecule self-assembly could both improve the surface flashover voltages and their combination could further improve the flashover voltages. The results demonstrate that molecule membrane and the micro grooves in the composite structure can form dual suppression on the development of the vacuum flashover.