Abstract: Based on the characteristics of erosive storm and soil sheet erosion in the Loess area,the transportation system of the steady siltladen flow is used to simulate runoff and sediment generation from upper slope.The hydraulic characteristics of the silt-laden flow in different gradient grassplots and the mechanism of its reducing sediment are analyzed.The results show that the Froude number Fr of the different gradient grassplots with the overland flow increases with the increase of the gradient,and the silt-laden flows of all treatments are laminar and tranquil.The roughness coefficients decreases with the increase of the gradient.There is a negative relationship between the grassland retention of the sediment and the gradient.And for the same gradient,grassplots reduce more sediment at the initial than final stage of the runoff generation.The sediment produced from grassplots has significantly greater mean diameter and proportion of the large particle (> 10 μ m) than that flowing into the grassplots under the same gradient condition.