The sediment yield caused by rill erosion is the main source of sediment yield in the water-wind erosion crisscross region of the Loess Plateau. It is of great scientific significance and practical value to make clear the characteristics of rill erosion process and its influencing factors in this region, so as to effectively prevent and control sediment entering the Yellow River and effectively maintain the safety of the watershed. In this study, the typical aeolian sandy soil on the underlying surface in the water-wind erosion crisscross region was selected as test soil, and the indoor flume scouring experiments with different flow discharges (3, 5, 7,9, 11 L/min) and different slope gradients (9°, 12°, 15°, 18°, 21°) were carried out, so as to establish equations, which could quantitatively reveal the response of rill detachment capacity to slope gradient, flow discharge and flow velocity. The results showed that: (1) The responses of detachment capacity to slope gradient and to flow discharge were both linearly and positively correlated, and the correlation were significant. The influence of flow discharge on detachment capacity was greater than that of slope gradient. In addition, detachment capacity was also affected by the superposition effect of slope gradient and flow discharge. The order of the influences on detachment capacity were: flow discharge, superposition effect of slope gradient and flow discharge, slope gradient. The relationships between detachment capacity and above three factors could also be well expressed by linearly positive correlations. (2) Flow velocity could be used as a key factor to reflect the superposition effect between slope gradient and flow discharge. There was a significant positively linear correlation between rill detachment capacity and flow velocity. Under the experimental conditions, the critical velocity was 0.607 m/s. (3) The four detachment capacity equations under the combination of slope gradient and flow discharge, under the combination of slope gradient, flow discharge and the superimposed effect of slope gradient and flow discharge, under the single flow velocity factor, and under the combination of slope gradient, flow discharge and flow velocity factor could predict and simulate the detachment capacity of aeolian sandy soil well, among which the equation considering the combination of slope gradient, flow discharge and the superimposed effect of slope gradient and flow discharge was the best. The results provide a theoretical basis for perfecting the rill erosion process model in water-wind erosion crisscross area.