Casium137 was uused to study soil erosion and sediment delivery on old sloping fields in Nan Xiao He gully of zst Gan Su on loess plateau in this papery. A quantitative analysis was made to test the soil erosion and sediment deivery. The results shown that the amount of erosion was high but delivery ratio in the slope was low. That is to say,the sediment that really lost from the land was less,so there was large amount deposition in old sloping fields. The soil loss can be reduced by constructing terrances. To compare terrance with the sloping fields,there is 96.5% benefit of reducing sediment.