Abstract: Abstract: We investigated the effects of soil crusts on soil erosion mechanism and their relationship, and series of the runoff scouring experiments were conducted in the Soil and Water Conservation Engineering Laboratory in Northwest A&F University. Two soil surface conditions-the crusts surface and the no crusts surface (control) were explored in our studies. The slope of the scouring trough was set up at 10°(17.6%), five flow rates (1.0, 1.4, 2.0, 2.4 and 2.8 L/min) were used to scour the soil. The flow velocity was measured by the staining method. The flow width was measured by a ruler on the top, central and bottom of slope. The water temperature was measured by a thermometer. The sediment discharge rate was collected at the end of the scouring trough. Then the hydrodynamic characteristics of overland flow (the average flow velocity, the average flow depth, the Reynolds number, the shear stress, the stream power and the resistance coefficient) and the relation between hydrodynamic characteristics of overland flow and soil erosion were analyzed. There was a significant effect of soil crusts on hydrodynamic characteristics. The Reynolds number under soil crusts surface was less than 500, which meant the overland flow was laminar flow. The flow velocity was greater on soil crusts surface than that without soil crusts surface, while the flow depth, the shear stress, the stream power and the soil erosion was much lower on soil crusts surface than that without soil crusts surface. The correlation between soil erosion and hydrodynamic characteristics of overland flow was significant (Regression coefficient R>0.90). Soil erosion had a positive linear correlation with Reynolds number and the logarithm of shear stress and stream power, while had a negative liner correlation with resistance coefficient. Therefore, the existence of soil crusts is helpful to reduce soil erosion from the runoff perspective. Due to the importance of the rainfall factor, it is better to study the effect of soil crusts on soil erosion by combing the raindrop splashing and runoff souring factors.