The combination of the fundamental measure theory (FMT) and the weighted correlation approach (WCA) within the framework of the density functional theory, i.e., the FMT/WCA approach, is applied to study the swelling pressure of Na-bentonite at different salt conditions. Good agreement between the FMT/WCA simulations and the results from both experiments and a Dorman-equilibrium-based DLVO model suggests that the hydration repulsion between charged surfaces can be well accounted by the ion-ion correlations effect.