To improve the surface vacuum insulating characteristics and the voltage withstand stability of the polymer insulator, pore-forming method on the surface of polymer insulators and its influence on the vacuum surface flashover voltages are studied by investigating the interaction between organic solvent-water mixed solvent and polymer materials. The organic solvent-water mixed solvent is applied to dispose the surface of the insulating material―polyetherimide. In the process, with the help of the organic solvent, water molecule is taken into the surface layer of the polymer. In the next solvent-remove process, the organic solvent is easy to get out of the polymer, leaving water molecule reuniting to water drops and occupying certain space in the body of the polymer. Finally, with the evaporation of the residual water drops under vacuum thermal treatment, micro holes are formed on the surface of the treated polymer insulator with chemical component unchanged. The results of the short-pulsed high-voltage test of the treated insulators indicate that the surface flashover voltages of the insulators increase effectively through the mixed solvent pore-forming treatment with proper organic solvent-water ratio. The method to create micro holes on the surface of polymer insulator is easy and appropriate to insulators with different geometric structures and scales.