Based on plot test of piling up top soil, the impacts of runoff on land productivity of sloping field is researched in Xiji county, semi arid hilly and gully region of the loess plateau. The results show that the lost runoff plays an important rule in the impacts of soil and water loss on land productivity of sloping field. Each 1 mm of lost runoff costs 9.7% of spring wheat output and 5.0% of potato, namely the impacts of lost runoff on spring wheat output of sloping field is half of that on potato. The impacts of lost runoff on spring wheat decreased by 41.7%～64.0% of its output in sloping field of different slope degrees and on potato decreases by 21.5%～33.0%. Impact of runoff on crops is 73.3% of the sloping field outputs every year and 16.3% of the total cultivated field.