Water flow resistance is one of the important hydraulic parameters.Elucidating the variations of rill flow resistance coefficient is critical to understand the hydraulic properties of rill flow and the mechanisms of dynamic rill erosion process.The flow resistance involved in rill erosion processes on loess hillslope was studied by a multi-plot experiment under simulated rainfall with addition of steady in-flow through the tops of the plots.The results showed that rill flow resistance coefficients for different rainfall intensities showed a consistently increasing tendency increase with runoff duration.Fifteen minutes after the initiation of runoff,the increasing trend changed and could be well described by an exponential equation.The resistance coefficients for different slopes exhibited the exactly same trend.The average resistance coefficient of rill flow decreased with increasing rainfall intensity,which can be described by a logarithmic equation,while it increased slightly with increasing slope steepness,which can be described by an exponential equation.A dual exponential equation can be used to describe the variations of the average resistance coefficient with various rainfall intensity and slope steepness.