Abstract: The vacuum outgassing of nonmetallic materials used for satellite may have a significant impact on the dielectric properties of the materials, thus increase the ESD risk of a long-term service satellite at a later stage. In this paper, the commonly-used non-metallic material (polyimide) is selected as the research object. The influence of outgassing on the surface potential of the polyimide samples is studied through the accelerated ground simulation test by a ⁹⁰Sr-⁹⁰Y radiation source, and the dielectric conductivity is calculated by curve fitting. It is found that in a high temperature vacuum environment under the 5 pA/cm² electron irradiation, the samples that have experienced longer time of degassing exhibit lower conductivity, about half of its original value at a total mass loss of 0.5%. The related physical mechanism is analyzed. The result may provide some guidance to the ESD protection design for long-lifetime satellites.