【Objective】This study aimed to investigate the relationship between the hydraulic characteristic parameters of rill erosion and the changes in microtopography of the eroded, which is an important mechanism for investigating rill erosion.【Method】In this study, the loess was selected as the research material, and four slopes gradients(5°, 10°, 15°, 20°) and four flow rates (2, 4, 8, 16 L·min-1) were set. The limited rills with a width of 0.1 m were used to simulate the rill erosion experiment, combined with Structure-from-Motion (SfM) photogrammetry, the relationship between the hydraulic characteristic parameters of rill erosion on slopes and microtopographic variation were analyzed.【Result】The results showed that under the experimental conditions, the flow velocity ranged from 0.23 to 0.92 m·s-1 and slope had a greater influence on flow velocity than the flow rate. The ranges for the Reynolds number and Froude number were from 255 to 2358 and 1.89 to 5.90, respectively. These hydraulic characteristic parameters increased with an increase in both slope and flow rate (P<0.05), while the resistance coefficient exhibited the opposite trend. Surface roughness, relief amplitude, and surface incision depth varied within the ranges of 0.33 to 2.35 cm, 0.47 to 4.35 cm, and 0.53 to 2.53 cm, respectively. The surface roughness, relief amplitude, and surface incision depth were positively correlated with flow velocity, Reynolds number, and Froude number, but negatively correlated with the resistance coefficient. Additionally, surface roughness, relief amplitude, and surface incision depth increased in linear and power function trends with increasing flow velocity and Reynolds number.【Conclusion】As the slope and flow rate increased, all hydraulic characteristic parameters and microtopography factors of the eroded, except for the resistance coefficient, showed a significant increasing trend, indicating that the microtopography was evolving towards conditions that favored erosion. The surface roughness, relief amplitude, and surface incision depth showed a significant positive correlation with changes in flow velocity and Reynolds number. Additionally, the responses of these three microtopographic factors to changes in flow velocity and Reynolds number followed linear and power function relationships. When the flow was low, the variation in surface roughness was the greatest. As the flow rate increased, both the surface relief and the surface incision depth gradually increased, indicating that the downcutting effect of runoff during the erosion process was intense, leading to a continuous increase in rill erosion depth. Our research results can provide a theoretical basis for the control of soil and water loss in loess slope cultivated land and the study of regional ecological restoration.