Abstract: Soil detachment from rill bed decreases with increase in sediment concentration in the flow, as many erosion models such as WEPP suggested. Using a typical silt-clay soil from the Loess Plateau, a series of 405 flume experiments were conducted, on slopes of 5°, 10°, 15°, 20° and 25°, flow rates of 2, 4, 8 L/min and rill lengths of 0.5, 1, 2, 3, 4, 5, 6, 7, 8 m, with 3 replicates for each to determine quantitatively the relationships between sediment load of water flow and rill length under different slope steepnesses and flow rates. Based on the experiments thus made, a method was advanced to compute the detachment rate of sediment loading water flow, under the assumption that the flow and soil are behaving the same way along rills. Then detachment rates were presented as functions of sediment concentration and rill length.