In order to study the hydraulics parameters for representative Loessal soil slope in western Shanxi province, and reveal the hydrodynamic mechanism of erosion and sediment yield by slope shallow overland flow under indoor artificial rainfall simulation, five slope lengths(1,2,3,4,5 m) with 4 rainfall intensities(30,60,80,125 mm/h) were used under a specific slope(20°). Reynolds number, Froude number, flow velocity, runoff depth and runoff shear stress were measured and analyzed. Results indicated that the flow pattern is basically laminar flow and torrential flow within designed rainfall intensities and slope lengths, the runoff turbulence is stronger with increasing slope length and rainfall intensity, therefore, the effect of slope length on hedgerows space should be considered. The slope length and rainfall intensity both have a significant influence on mean runoff depth, velocity, shear stress, and the impact of rainfall intensity on three parameters is greater than the slope length. Shear stress is linearly related to slope length and rainfall intensity(R2>0.89), however, when both of them act on the shear stress, there are some mutual constraints. The conclusion provides theoretical basis for the soil erosion of Loessal soil slope in western Shanxi Province.