[Objective] The objective of this study was to reveal the variation patterns of rill sediment transport capacity with slope gradient and flow rate, improve the sediment transport theory, and construct soil erosion prediction models. [Methods] Through indoor flume tests with added soil, the rill sediment transport capacity of four typical soils on the Loess Plateau（silty clay, sandy loam, silty loam and silt） was measured under combinations of five slope gradients（9°, 12°, 15°, 18° and 21°） and four flow rates（5, 7, 9 and 11 L/min）. The trends in rill sediment transport capacity with slope gradient and flow rate for four soils were analyzed, and prediction models for rill sediment transport capacity were developed.[Results] 1) The rill sediment transport capacity of the four soils increased with increasing slope gradient or flow rate. At a slope of 15° or under flow rates of 7, 9 and 11 L/min, significant differences were observed in the rill sediment transport capacity among the four soil types（p＜0.05）. 2) The rate of increase in rill sediment transport capacity among the four soil types exhibited a nonlinear trend between adjacent slope gradients（or flow rates）. 3) The response of rill sediment transport capacity to slope gradient（or flow rate） for different soils under varying slope gradients（or flow rates） could be well described by power functions（R²: 0.713-1.000）. Given that rill sediment transport capacity was influenced by the coupling effect between slope gradient and flow rate, binary exponential function-based prediction models for rill sediment transport capacity were developed for the four soils, with both slope gradient and flow rate being incorporated as variables. The constructed models all exhibited high predictive accuracy（R²: 0.839-0.945）. [Conclusion] The rill sediment transport capacity exhibits complex response to slope gradient and flow rate for four soils on the Loess Plateau. The power function model demonstrates superiority in characterizing the response of rill sediment transport capacity to slope gradient or flow rate.