Design and manufacture of pulse power equipment greatly depend on the investigation of flashover on dielectric surface in vacuum under pulsed voltage. It is expected that sputtering coating with semiconductivity and high thermal conductivity can apparently improve the surface flashover characteristic of dielectric materials. Three kinds of thin films (TiO₂, ZrO₂ and HfO₂) were sputtered on epoxy substrate using magnetron sputtering in ultrahigh vacuum. Experiments were carried out under high voltage pulse (50ns rise time and 600ns full width at half maximum) in vacuum to study the flashover characteristics of three kinds of oxide films. The experimental results show that the TiO₂, ZrO₂ films sputtered on the epoxy substrate are amorphous as they are not annealed and surface grains are not crystalized, but HfO₂ film becomes crystalized. The flashover voltage of TiO₂ film is the highest, the flashover voltage of HfO₂ film is close to the epoxy sample. The effect of puttering time on the flashover voltage is different for different target materials. The vacuum flashover voltage increases with the sputtering time increasing for TiO₂ and HfO₂ films, but decreases for ZrO₂ film. Furthermore, the effects of film properties on flashover performance as well as the distribution of surface charge after flashover are analyzed.