Abstract: Flow velocity is of great significance to understanding the process of inter-rill erosion and hydrology on a hill slope under rainfall conditions,which is an important parameter for hydrology and soil erosion modeling.A solute centroid method is employed to measure the velocity distribution of sheet flow based on solute transport process,to understand the influence of straw mulching on flow velocity.The measurements are made at slope lengths of 3,5,6 and 7 m under rainfall intensities of 80,120 and 160 mm/h,straw mulching quantities of 2and 8 t/hm~2,and slope gradient of 10°.The measurements clearly indicate that flow velocity is significantly affected by rainfall intensity and straw mulching quantity.In this paper,the velocity of sheet flow ranges from 0.016 to 0.108 m/s,increases with rainfall intensity,and decreases with straw mulching quantity.Flow velocity increases with the slope length,while the increase rate slows down before approaching a steady velocity.The distance for sheet flow velocity to reach its maximum becomes shorter under greater rainfall intensity and straw mulching quantity.This paper helps understand the hillslope hydrodynamics along the mulched slope under rainfall conditions.