Abstract: The technique of using geogrid-reinforced expansive soil as cover layer to protect expansive soil slopes belongs to the “covering” category in expansive soil reinforcing techniques and is mainly used for preventing shallow failure of expansive soil slopes. This technique has been widely used in expansive soil regions in China in recent years. However, the hydromechanical responses of the geogrid-reinforced layer deserves further investigation. This paper presents a case study on an expansive soil slope reinforced using this technique at the Chongzuo-Aidian Road. The distribution and evolution of the moisture content and horizontal earth pressure of the expansive soil and the tensile strain of the geogrids within the reinforced layer were monitored for three years for analyses. Based on this, numerical simulation studies were conducted to model the slope in the case study and further investigate the hydromechanical responses and stability of the slope upon infiltration. The results demonstrate that (i) the reinforced layer is effective in isolating the influences of external wetting and drying impacts and keep the moisture content stable in the underlying natural expansive soils. It has the function of humidity maintenance; (ii) upon drying-wetting cycles, the maximum strain of the geogrids is at the middle of the reinforced layer, and the horizontal earth pressure in the reinforced expansive soil increases with the distance to the slope surface; (iii) through reinforcement and the wrapping of the expansive soil, the geogrids improve the integrity and shear resistance of the reinforced layer and restrain the swelling strain. Therefore, although expansive soils loss strength over drying-wetting and may cause shallow failure for unreinforced slopes, the reinforced cover layer remains stable.