The slope flow state in rill erosion process on loess hillslope were studied by a multi-plot experiments under simulated rainfall. The results showed that: 1) the rill flow Froude number(Fr), a judging index of flow state, decreased with rainfall intensity and slope. The exponential equation could describe the trend. 2) The average Fr of rill flow increased with increasing rainfall intensity or slope, which could be described by the power function equation and exponential equation respectively, while could be described by a dual exponential equation to both factors. 3) The average Fr varied between 6.309 and 7.336, indicating that rill flow was rapid.