Abstract: Based on the Monte Carlo method and the finite element method (FEM), a method is proposed to calculate the internal charging process of the two-layer and four-layer printed circuit boards (PCB) with the copper layer grounded by the electric resistance. We discuss the isotropic source of electrons in the Geant4 program, the grounding boundary condition by the electric resistance, and how to build the finite element matrix function. We calculate the impact of the electric resistance on the charging process, and it is shown that the resistance can increase the electric field and the potential as compared with the fully-grounded situation. Accordingly, the maximum electric field value changes. The calculation also shows that the electric potential of the layer which is not fully-grounded is in a linear relation with the resistance. When the resistance is about 10⁹ Ω or smaller, its impact on the internal charging can be ignored. This result validates the applicability of guidelines in NASA-HDBK-4002A.