The flow shear stress involved in rill erosion process on loess hillslope and its effect were studied by multi-plot experiments under simulated rainfall with addition of steady inflow through the tops of the plot.The results showed that:(1)The rill flow shear stress increased along with time under different rainfall intensities and the relationship could be described well with a linear equation.The rate of increase was a little less in 6 min after than before.(2)Under different slopes,it increased basically in the same trend and an equation of the straight line could be used to describe the change.The rate of increase appeared difference when runoff began after 12 min.(3)The shear stress of average slope rill flow increased with rainfall intencity and rapidly increased with slope. Its relation to rainfall intensity could be described by a logarithmic equation;to slope,by a power function equation;and to both of the two factors,by a dual power function equation.(4)Under different rainfall intensity and slope,the rill erosion rate increased along with the rill flow shear stress and the relationship could be described well with a linear equation.The shear stress of rill flow,that had significant erosion effect,was one of the important hydraulic parameters and hydrodynamic source of rill erosion.