Based on the measured data and the model of plotted watershed hydrology,the benefits of water reduction by different harnesses of soil and water conservation are firstly separated in watershed scale,which are the basis of evaluating the effect of rebuilding ecological environment of the loess plateau on the water resources of the Yellow river. The results indicate that the benefit of watershed water reduction by engineering harness of soil and water conservation was 18. 1%on what had been achieved in the period of the sixth five-year plan,and that the benefit by ecological and agricultural harnessof soil and water conservation was 10.9 %on what had been achieved in the period of the seventh five-year plan. For reducing the effect of ecological and environmental construction in the loess plateau on water resources of the Yellow river,the ecological and agricultural harnesses should be main measurements.