To simulate the soil water movement process of deformable soils, a modified Richards model considering soil deformation (RMSD) was established. In the model, new parameters were introduced, including deformable soil porosity, deformable soil saturated hydraulic conductivity and unsaturated hydraulic conductivity of expansive soils, which varied with soil depth and time under the effect of soil deformation. The newly introduced parameters originated from physical properties of the soils and their calculation formulas were suggested. One-dimensional infiltration–runoff experiments were performed to evaluate the performance of the RMSD. The results showed that average relative errors (ARE) of simulated runoff intensity and cumulative infiltration (by the RMSD) ranged from −10.0% to −1.0% and from −1.0% to 11.0%, respectively, and Nash efficiency coefficients (NSE) of simulated cumulative infiltration (by the RMSD) were larger than 0.90. As the RMSD model is much better than the traditional Richards model (TRID) in fitting the observations of soil cumulative infiltration and runoff intensity, it is believed that the newly suggested model provides a suitable tool to depict the soil water movement in deformable soils.