Abstract: Sand and clay sediments are studied by means of ¹³⁷Cs tracing test in typical grass-covered peak cluster depression in Maolan, southern Guizhou. It proves that：The grass-coveted soil profile in depression is formed by aecumulation, and the ¹³⁷Cs concentration variation with the depth of the profile reflects the information of sediment accumulation and surface soil erosion. Affected by earth-rock distribution and micro topography, the spatial redistribution of the ¹³⁷Cs after primary fallout is uneven, and ¹³⁷Cs inventories occurs greater spatial variation with the variation coefficient being 1.35, which shows that the ^137Cs inventory can not characterize the status of soil erosion. According to the ¹³⁷Cs concentration distribution along a typical profile A-1 , the sediment accumulation rate and the natural surface soil erosion rate are respectively 16. 6 t/ km^2 · a and 45.95 t/km^2 · a, which shows that about 63.88% of the eroded surface soil is removed by way of underground loss. The relative contribution ratio of surface soil loss and underground soil loss are respectively 70. 13% and 29.87%. By comparison to the utmost soil formation rate 13.51 t/km^2 · a in Maolan, the risk of soil erosion in the Engineering Monument grass-covered depression is higher.