Transport capacity of flowing water in a rill is one of the important parameters in soil erosion,especially in soil erosion prediction and soil erosion process modeling.Considering the fact that,under steady flow,sediment load increases with slope length and will finally approach the transport capacity,a laboratory flume experimental method with variable slope length is advanced for transport capacity determination. And a mathematical expression is suggested to estimate transport capacity with thus obtained experimental data.A series of 405 flume experiments were conducted with sand-clay(loess) soil.Transport capacity is related to slope and inflow rate,based on the experimental data under five slopes (5°,10°,15°,20°,25°),and three flow rates(2,4,8Lmin^-1).