A plough pan with reduced permeability accumulates infiltrated water along slopes then saturates the cultivated layer under continuous rain. Topsoil saturation is a frequent phenomenon and an important process of the special soil slopes. A methodology and device system was used in this study to keep cultivated purple soil saturated. Strands of scouring tests were developed to quantify the rill erosion and sediment transport processes along a saturated purple soil slope at four experiment slopes (5°, 10°, 15°, and 20°) and three flow discharges (2, 4, and 8 L·min⁻¹). The experimental results indicated that the sediment transport capacity on a saturated purple soil slope ranged from 0.03 to 1.56 kg·s⁻¹·m⁻¹ with the increasing trend along the slope gradient and flow discharge, and the increasing trend could be well matched by a nonlinear multivariable equation. The sediment concentration of the saturated purple soil slope exponentially increased with rill length and decreased with the increment rate, and the maximum sediment concentrations observed in this study in different hydraulic events ranged from 108.13 to 1174.20 kg·m⁻³. Saturated and non-saturated purple soil slopes erode differently with the maximum sediment concentration of saturated purple soil slope recorded at approximately 1.42–2.10 times the values for non-saturated purple soil slope. The findings of this research help illustrate the sediment transportation and erosion behaviors of a saturated purple soil slope and serve as the basis for determining the parameters in the erosion models of the purple soil slope.