The aim of this paper is to show the impacts of the vertical discretization in a physical soil numerical model on the calculation of the heat and mass transfer equations. The Simple Soil Plant Atmosphere Transfer (SISPAT) model was used in this study. It solves the coupled equations of mass and energy transfers in the soil and can deal with several horizons for vertically non-homogeneous soils. A series of numerical experiments have been performed to assess the influence of the vertical resolution grid on the simulation of the heat and water transfers using the SISPAT model in a one horizon configuration (homogeneous soil). In the studied case, a minimum of 20 layers has been found for a single 1.4 m thick horizon. Based on this analysis, numerical tests have been performed using SISPAT in a four horizons configuration. Key words: soil–atmosphere exchanges, numerical model, vertical resolution, heat and mass transfer.