Abstract: The enhancement of high-energy electrons flux near a mono-energy often occurs in geosynchronous orbit, and a large number of electrons injection leads to a more significant charging effect of spacecraft dielectric. To better evaluate the internal charging level of spacecraft dielectric in geosynchronous orbit under the mono-energetic electron enhancement phenomenon, a 3 mm-thick flat plate three-dimensional model of spacecraft media polyimide was established in this paper, and a Geant4-COMSOL joint charging evaluation method based on the numerical calculation of high-energy electron radiation and internal electric field was adopted. The charge deposition rate and radiation dose rate distributions of polyimide under 0.4, 0.7, 1.0 and 1.3 MeV mono-energetic electrons and FLUMIC electronic environment energy spectrum radiation in geosynchronous orbit were obtained, at the same time, the internal electric field strength and potential distribution were calculated. The mono-energetic electron and FLUMIC energy spectrum were superimposed to study the internal electric field and potential distribution of polyimide. The effects of radiation conditions and material properties on the potential and electric field were analyzed through charge transfer process. The results show that, under the specific insulation structure, 0.7 MeV monoenergetic electron incidence generates the highest potential, while the electric field intensity generated by 1.0 MeV monoenergetic electron incident is the highest. When mono-energetic electron enhancement occurs in geosynchronous orbit, the 1.0 MeV electron enhancement increases the electric field intensity, but the 1.3 MeV electron weakens the electric field intensity. Based on the charge transfer process, the charging law under superposition environment is explained. The study shows that, when the mono-energetic electron enhancement occurs in the insulating medium of a specific structure in the geosynchronous orbit, the injection of electrons will lead to the strengthening of the charging effect, which will result in the worst case, and the higher electron energy will penetrate the material and improve the dielectric conductivity, effectively reducing the internal electric field of the material.