Flow velocity is one of the most basic and important hydraulic parameters. Clarifying the variation of rill flow velocity is of importance to reveal the mechanisms of dynamic rill erosion processes. Rill flow ve-locity on loess hillslope is studied through a multi-plot experiment under simulated rainfall with the addition of a steady in-flow at the top of the multi-plot system. The main findings are as follows:(1)Rill flow veloci-ties for different rainfall intensities decrease with runoff duration, which can be well described by an expo-nential equation.The decrements are great 6 min after runoff generation and then decline. The tendencies arebasically consistent for the decrements at different intensities. (2)Rill flow velocities for different slopes also decrease with runoff duration, which can be described by an exponential equation.The tendencies for the decrements on different slopes are consistent. The decrements are basically consistent during the whole run-off process. (3)The mean flow velocity increases with increased rainfall intensity, which can be well de-scribed by a logarithmic equation, and increases with increased slope steepness, which can be well described by apower equation. A dual logarithmic equation can be used to describe the variation of the mean flow ve-locity with rainfall intensity and slope