Though Series-Mixing-Cell-Model (SMCM) has been widely used in modeling solute transport and reactions, it's mainly for saturated conditions. Therefore, SMCM was extended to simulate salt movement during leaching process of initial unsaturated soils, by employing Kostiakov equation and piston assumption to describe water movement during infiltration. An analytic solution of the extended model was derived and analysis showed that, for given soil types, initial water and salt content profiles, simulation results would be influenced by layer thickness, and there was a quantitative relationship between optimized layer thickness, saturated hydraulic conductivity and solute diffusion coefficient. When layer thickness was chosen appropriately, results of this extended model were close to those of HYDRUS-1D. Further, the extended model was validated by experiment data, which showed that this model has advantages such as a small number of parameters which could be easily acquired and reasonably accurate modeling results.