Deep dielectric charging and discharge is one of the most harmful factors for spacecraft. In this paper，by using GEANT4-RIC method，the deep dielectric charging electric field of 2.0 mm thickness circuit board is calculated under the worst-case internal spectrum in Geostationary Earth Orbit(GEO) from NASA4002A. The simulation result shows that the maximum dielectric charging electric field decreases exponentially with the increasing of the thickness of the shielding layer. When the thickness of the shielding layer is above 1.4 mm Al，the maximum electric field is below 106 V/m，which shows no deep dielectric discharge hazard.