A dual box system, consisting of a 2 m long feeder box and a 5 m long test box with 150 gradient was used to quantify effects of run on water and sediment on rill erosion process at down slope section and rill flow hydraulics parameters, as well as relationship of rill flow hydraulics parameters and sediment delivery by rill erosion. The results showed that detachment transport was dominated in rill erosion processes, runoff from up slope always caused additional sediment delivery in the rill box, the additional sediment delivery increased with a decrease of sediment concentration in runoff from the feeder box and an increase of rainfall intensity. Up slope runoff discharging into rill channel at down slope section or an increase of rainfall intensity resulted in that rill flow shifted from stratum flow into turbulent flow. Runoff from up slope had an important effect on rill flow hydraulics parameters, such as rill flow velocity, Reynolds number and Daycy weisbach coefficient. The relation between rill flow hydraulics parameters and additional sediment in rill channel caused by up slope runoff was analyzed. And a statistic model among the additional sediment in rill channel and relative increment of rill flow velocity and Reynolds number, as well as relative decrement of rill flow Daycy weisbach coefficient was established.