Grass coverage has great influence on the stay of overland flow.The objective of this study is to reveal the influence of grass coverage on the time of runoff beginning and stop in the hillslope-gully slope erosion system on loess hilly area.In scouring experiments,five grass coverage degrees(0,30%,50%,70% and 90%),three spatial distributions of grass on the hillslope(upper,middle and lower) and two water inflow rates(3.2 L/min and 5.2 L/min) were used in the experimental soil box for the hillslope-gully slope erosion system experiment and the single hillslope experiment.Results showed that in the scouring experiments the time of runoff beginning has a negative relationship with the water inflow rate,and has a positive relationship with the grass coverage percentage.The time of runoff stop has a positive relationship with the water inflow rate and the grass coverage percentage.The delaying role of grass coverage on runoff increased with increasing grass coverage percentages and decreased with increasing water inflow rates.Usually,when the grass coverage was located on the upper and middle sections,the delaying role is relatively larger.