Abstract: The microstructure of clay, the surface electric field of clay particles and the interaction of ions have great effect on the ion transport. However, the problem of how to consider the effect on ion the transport by the electric field hasn't been solved. The Nernst-Planck equation is combined with the Poisson equation to describe the ion transport in charged clay soils at the microscale. The combined equation simultaneously considers the coupling influence of the concentration field and static-electric field on the ion transport. A finite element model is set up based on experimental results. The numerical analysis indicates that cation concentration visibly increases due to a particle negative charged attraction, on the other hand, anion concentration reduces due to charged repel. But the traditional method does not take into account the influence of a particle charged, because the distribution of the cation is the same as that of the anion concentration. Double-layer is obviously formed on the particle surface, the higher the concentration, the thinner the thickness of double-layer; the lower the concentration, the thicker the thickness of double-layer. The analytic results will be important to in-depth understanding of the coupling influence between the concentration field and static electric field during the ion transport. The research macroscopically provides the exhaustive foundation data for further analysis.