A distributed eco-hydrological process-based model was developed to simulate the water budget and vegetation productivity in the Wuding River basin, Loess Plateau, under the scenarios of historical and future climate. Since the mid of last century, the annual mean of air temperature tended to increase and precipitation appeared no tendency, but with a lower amplitude of annual variation in the basin. Correspondently, the actual evapotranspiration had similar tendency with precipitation. However, the vegetation net primary productivity (NPP) increased with a rate of 0.6 gC m^-2 a^-1, and water use efficiency increases due to fertilization of air CO₂ enrichment. Under the HadCM3 climate scenario in the 21st century, the simulated results show that the actual evapotranspiration, surface runoff, vegetation NPP and water use efficiency will increase significantly.