Rill erosion is one of the most important slope erosion in loess area, and soil detachment process is an important link of rill erosion. However, the existing studies only are based on a single soil conditions, while the simple relationship between soil detachment rate and water dynamics cannot fully reflect the coupling mechanism of the soil detachment rate under different types of soil. More importantly, the existing research involves little on the relationship between the detachment rate and bed surface morphology. The article adopted the combination of six kinds of slope gradients (2°, 4°, 6°, 8°, 10° and 12°) and five discharges (8L/min, 16L/min, 24L/min, 32L/min, 40L/min) to do scouring experiment. The results showed that: soil detachment rate had power function relationship with discharge and slope, and slope had a greater influence than discharge; Different types of nondimensional soil detachment rate and nondimensional unit stream power had zoned phenomenon with nondimensional flow velocity which showed that soil detachment had other influence factors except diameter of particles; Nondimensional soil detachment rate and nondimensional shear stress doublelog function had a linear increase relationship, and there was no partition; Soil detachment rate had a trend of increase power function with the increase of down hole development coefficient, and the soil detachment rate had a power function decreasing trend with the L/H increases. This results show that the more complex bed surface morphology increased, the more mature down hole developed increasingly and the more intense soil detachment is. The results of the study have some theoretical value to the mechanism of sediment transport on rill flow erosion, moreover it has a certain guiding significance on loess slope surface soil detachment control and ecological restoration.