Abstract: Grass coverage has great influence on the change of overland flow velocity. Studies on the temporal and spatial distribution characteristics in overland flow process with different grass coverage degrees are necessary to better understand and reveal the soil loss reducing mechanism of grass coverage. The objective of this study is to reveal the changeable process and characteristics of overland flow velocity with different grass coverages in the slope-gully system on Loess Hilly Area. Five grass coverage degrees (0, 30%, 50%, 70% and 90%), three spatial distributions of grass (upper, middle and lower) and two water inflow rates (3.2 L/min and 5.2 L/min) were adopted in the experimental soil box. Results showed that the grass coverage had great influence on staying flow velocity at 3.2 L/min inflow rates, which was relatively weak for 5.2 L/min inflow rates. An exponential relationship between the flow velocity and grass coverage degree is observed. The flow velocity increased and reached the maximum on the hillslope within a three or four meters' downslope distance, and the flow velocities of each segment almost all decreased with increasing scouring duration in the scouring experiments.