The ¹³⁷Cs tracing technique was applied to the study of soil erosion in the Nangou watershed on the Loess Plateau. The results showed the soil erosion rate was high in lands under all types of land use on the Loess Plateau. Compared with uncultivated soil, cultivated land suffered higher soil erosion. Based on the special soil properties, the soils in the Loess Plateau ought to be sorted into the class of severe soil erosion.