In recent years,the tracing method of rare earth element(REE)has been used to study the dynamic processes of soil erosion,such as its initiation,development and distribution upon the hill slope.A series of laboratory rainfall simulation experiments were conducted with eight REEs,namely Dy,La,Sm,Yb,Ce,Eu,Nd and Tb.The experiments involved 3 rainfall intensities:50 mm h^-1,100 mm h^-1 and 150 mm h^-1;4 slope gradients:8.74%,17.63%,36.4% and 46.63%,with 3 replicates.The REE experiments revealed soil erosion distribution and its relation to the development of eroding rills.Analysis was made to relate the fluctuation in soil erosion upon the slope to the energy in the runoff flow.With quantitative determination of soil erosion along slope by REE tracers,the critical distance at which rill erosion initiated was determined,and the critical shear stress of soil were estimated accordingly.Regression analyses of maximum rill detachment rate and shear stress and stream power of runoff were made.