The flow patterns involved in rill erosion process on loess hillslope are studied by a multi-plot experiments under simulated rainfall with addition of steady in-flow through the tops of the plot. The results showed that: (1) The Reynolds number of rill flow

a judging index of flow pattern

changed under different rainfall intensities and slopes with a overall rise and finally a stabilized trend. A power function equation can be used to describe the two processes. (2) The average Reynolds number of slope rill flow increases with rainfall intensity and slope. Its relation to both rainfall intensity and slope can be described by a logarithmic equation; and to both of the two factors

by a dual power function equation. (3) The rill flow pattern is the laminar flow under different rainfall intensities and slopes. Only under the two of the largest rainfall intensities and slopes

rill flow may be in the transition region. (4) The average Reynolds number

a measure of fluid turbulence

varies between 327 and 457 and remains in the regime of normally considered laminar flow. The change of the Reynolds number

with the amount of the flow

is a significant positive linear correlation.