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Studies on rill morphological characteristics can reveal soil erosion mechanisms, and rill morphology has important influence on runoff and soil loss of the hill slope. However, the existing studies only use rill density, rill width-depth ratio, etc. to characterize rill morphology, which cannot fully reflect rill morphological characteristics. Effects of rainfall intensity and slope gradient on rill erosion and rill morphology at the loess hill slope were studied based on a rainfall simulation study. The experimental treatments included three rainfall intensities (50, 75 and 100mm/h) of representative erosive rainfall on the Loess Plateau and three common slope gradients (10°, 15° and 20°) of rill erosion occurrence. The results showed that both soil erosion and rill erosion increased with increasing of rainfall intensity and slope gradient, where relationships among them were the power function. Rill inclination angle concentrated between 16°~20° under the experimental conditions, and it increased with an increase in rainfall intensity and decreased with an increase in slope gradient. Rill density, degree of rill dissection and rill tortuosity complexity were 0.74~1.95m/m2, 0.08~0.17 and 1.09~1.38, respectively, which all increased as rainfall intensity and slope gradient increased. Rill width-depth ratio was 1.93~2.35, which decreased with increasing rainfall intensity and slope gradient. By analyzing correlations between rill erosion and rill morphological indicators, degree of rill dissection is the best indicator to evaluate rill erosion and rill morphology. When studying the effect of rainfall intensity on rill morphology, indicators of degree of rill dissection, rill tortuosity complexity and rill inclination angle are recommended to preferentially select. When analyzing the effect of slope gradient on rill morphology, indicators of rill density and rill width-depth ratio are recommended to preferentially select, except for degree of rill dissection. Most of rill cross sections presented “V” shapes. Generally, the rill cross section appeared more and more irregular change with increasing rainfall intensity and slope gradient, where the runoff turbulence increased. This indicated that the change of rill cross section can reflect change characteristics of runoff, thereby reveal the rill erosion mechanisms.