Rill erosion is a critical process in hillslope soil and water loss; however, the characteristics and intrinsic mechanisms of hillslope rill erosion remain unclear. In this study, intermittent rainfall simulations on indoor soil flumes examined linkages between hillslope rill erosion sediment yield, hydrodynamics, and morphological evolution in the Loess Plateau's wind-water erosion crisscross region. Four rainfall intensities (1.0, 1.5, 2.0, and 2.5 mm min(-1)) and two typical soil slope conditions (loess slope and sand-covered slope) were investigated. The results indicated that rill erosion significantly contributed to total hillslope soil erosion, with the total contribution rates ranging from 67.02 % to 78.13 % for the loess slope and from 58.54 % to 73.56 % for the sand-covered slope. The analysis of hydrodynamic parameters revealed that the critical flow velocity, critical shear stress, critical stream power, and critical unit stream power for the loess slope were 0.061 m s(-1), 0.459 Pa, 0.036 N m(-1) s(-1), and 0.013 m s(-1), respectively. The corresponding critical hydrodynamic parameters for the sand-covered slope were consistently lower than those of the loess slope. Meanwhile, linear regression analysis was employed to investigate the relationships between hydrodynamic parameters and soil erosion rates. Results indicated that stream power provided stronger explanatory capability for soil erosion processes on loess slopes (R-2 = 0.642, p < 0.01), whereas shear stress better described the erosion processes on sand-covered slopes (R-2 = 0.595, p < 0.01). In addition, among the rill morphological parameters, the maximum rill length (M-RL) and maximum rill width (M-RW) were identified as the dominant factors influencing soil loss on loess slopes and sand-covered slopes, with respective contribution rates of 30.3 % and 39.6 %. In summary, this study offers theoretical insights into the hydrodynamic thresholds and morphological controls of rill initiation and development, thereby deepening our understanding of slope erosion processes.