Soil water content plays a vital role on both hydrological and ecological processes, especially in semiarid ecosystems where precipitation represents the main water source for local plants, such as Beijing. This study tries to explore the ecohydrological functions of the soil water balance through a distributed modeling approach. A soil water balance model was developed for the Yanqing Basin in northwest of Beijing. It accounts for precipitation, runoff, and evapotranspiration and simulates the soil water content at basin scale from January 1981 to December 2005. The soil water deficit, i.e. water stress was computed spatially and temporally. It was used as an indicator for interpreting the vegetation dynamics of this area. While the potential aquifer recharge computed from the soil water balance model demonstrated how the soil impacted on groundwater system. The results give a quantitative evaluation on how soil water content impacted by climate change while how it influence on hydrological and ecological processes.