The 26 soil samples in a small watershed of Yangtse delta region have been collected and its contents of 137 Cs have been determined. The results showed that the relationship between amounts of 137 Cs and depth of sampled soils is near linear (0.98>R 2>0.69). Based on the value of 137 Cs on the top of hill, we considered that 2 400 Bq/m 2 137 Cs is probably the background value in the region. Eventually, soil erosion and deposition was calculated,the amount of soil erosion on middle hill accounts for 38.23% of total erosion, and the value of vegatable soil occupy its 32.89%. Therefore, we should take some measures to provent the soil loss in this region.