In the rill erosion process, run--on water and sediment from upslope areas, and rill flow hydraulicparameters have significant effects on sediment detachment and transport. However, there is a lackof data to quatify the effects of run--on water and sedimeni and rill flow hydraulic parameters on rillerosion process at steep hillslopes, especially in the Loess Plateau of China. A dua1--box system,consisting of a 2--m--long feeder box and a 5--m--long test box with 26.8% slope gradient was used toquantify the effects of upslope runoff and sediment, and of rill flow hydraulic parameters on the rillerosion process. The results showed that detachment--transport was dominated in rill erosionprocesses; upslope runoff always caused the net rill detachment at the downslope rill flow channel,and the net rill detachment caused by upslope runoff increased with a decrease of runoff sedimentconcentration from the feeder box or an increase of rainfall intensity. Upslope runoff discharginginto the rill flow channel or a In the rill erosion process, run - on water and sediment from upslope areas, and rill flow hydraulic parameters have significant effects on sediment detachment and transport. However, there is a lack of data to quatify the effects of run - on water and sedimeni and rill flow hydraulic parameters on rillerosion process at steep hillslopes, especially in the Loess Plateau of China. A dua1 - box system, consisting of a 2 - m - long feeder box and a 5 - m - long test box with 26.8% slope gradient was used toquantify the effects of upslope runoff and sediment, and of rill flow hydraulic parameters on the rillerosion process. The results showed that detachment - transport was dominated in rill erosionprocesses; upslope runoff always caused the net rill detachment at the downslope rill flow channel, and the net rill detachment caused by upslope runoff increased with a decrease of runoff sedimentconcentration from the feeder box or an increase of rainfall intensity. Upslope runoff discharginginto the rill flow channel or a