In order to explore the drop pit development on soil-rock mixed colluvial deposit slopes, a scouring test was conducted in laboratory. Four soil-rock mixed colluviums (0, 10%, 30%, 50% gravel in mass ratio) under different flow discharges (2, 4, 8, 12 L/min) were tested.The results were as followed:the number of drop pit varied from 3 to 17, the average depth of drop pit was between 1.10 to 5.93 cm, and the profile form indices were between 2.97 and 19.97. The number of drop pit, the depth of drop pit, and the profile form indices all showed the increasing trend overall with the increase of scouring duration, whereas the maximum value appeared in some slopes at 5 min or 7.5 min. All drop pit parameters first increased and then decreased with the increase of flow discharge as a whole, and the maximum value appeared under the discharge of 8 L/min. The number of drop pit, the depth of drop pit, and the profile form indices increased with the increase of gravel content.The influence of flow discharge on the all parameters of drop pit was greater than those of gravel contents. Drop pit parameters were significantly correlated with flow velocity,resistance coefficient and Manning roughness coefficient. Shear stress was the best hydrodynamic parameter to describe the development of drop pit development as a linear function.