Based on the measured data and the model of plotted watershed hydrology, the benefit of sediment reduction by biological harnesses of soil and water conservation was studied in the watershed scale. The result indicated that the erosion modulus in Wangdonggou watershed, which were 1869 t.km-2, 1050 t.km-2, 383 t.km-2, and 504 t.km-2 in the periods of the sixth, seventh, eighth, and ninth five-year plans, respectively, were gradually reduced by comprehensive measures. Taken out the effect of rainfall, the sediment reduction by biological measures of soil and water conservation was increased by 24.1% and 22.4% in the periods of eighth and ninth five-year plans compared to that in the seventh five-year plan.