Abstract: Revealing the hydrodynamic characteristics is essentially important for understanding the internal mechanism of slope soil erosion. Through a series of simulated runoff scouring experiments conducted in riparian zones of the lower reaches of Yellow River, this paper studied the hydrodynamic process of soil erosion with overland flow on riparian slopes under four different slope gradients (5°, 10°, 15°, 20°) and three levels of vegetation coverage (0%, 15%, 30%) at the same scouring inflow rate (15 L·min^-1), meanwhile, we analyzed the changes of the hydrodynamic parameters, including the flow shear stress (τ), stream power (ω), and unit flow energy (F), and their responses to slope gradient, vegetation coverage and their interaction effects as well. The results indicated that τ, ω and F showed clear change rules under the effects of slope gradient and vegetation coverage. With fixed slope gradients, τ increased while ω and F decreased with the increase of vegetation coverage. Nonetheless, τ, ω and F all increased with the growth of slope gradient under the same vegetation coverage. The effect of changes in both slope gradient and vegetation coverage on soil erosion was insignificant on the slope less than 10°, while the effect of vegetation coverage on reducing soil erosion rate was obvious on the slope more than 10°. Similarly, the slope soil erosion yield aggravated significantly with the increase of slope gradient under the same vegetation coverage. Moreover, the soil erosion rate showed a good linear relationship with both τ and ω, and they both had critical flow shear stress and threshold stream power throughout the whole soil erosion process. F showed a good logarithmic relationship with soil erosion rate. Based on the double factor variance analysis, the effects of slope gradient and vegetation coverage on τ, ω and F were significant, while their interaction effect was significant only on ω, and insignificant on τ and F.