The simulation is one of the important methods to evaluate the internal charging risk in spacecraft. In this paper, based on the charge conservation law, a three-dimensional calculation model of the potential and electric field of internal charging is established, and the one-dimensional steady state and transient solution algorithm and the two-dimensional and three-dimensional solution scheme of the model are given. An interative algorithm is designed to solve the required conductivity and the electric field intensity, and the convergence of the interative algorithm is analyzed. Using the finite element algorithm and the local mesh refinement, the model has the advantage of easily investigating the electric field distortion at key points. Comparing with the existing radiation-induced conductivity (RIC) model, due to the fact that the internal charging time constant is much higher than the charge capture time and the trap density in the dielectric is much higher than the charge density after the charge balance, the free charge will be rapidly converted into the captured charge. Therefore, it is unnecessary to consider the charge capture mechanism in the RIC model. The CCL model can be used to evaluate the internal charging and has higher computational efficiency. Comparing with the experimental data, the correctness of the three-dimensional calculation model is verified. It provides a means to evaluate the dielectric internal charging in spacecraft.