【Objective】 The southwestern karst region is characterized by both geological fragility and sensitivity, with soil erosion being a significant concern. Biological soil crusts, as widely developed surface coverings, play a crucial role in regulating soil erosion. However, the underlying mechanisms of how biocrusts coverages at varying levels influence soil detachment control under different lithological conditions remain unclear. Therefore, it is essential to investigate the effects of different levels of biocrusts coverages on the process of soil detachment and the main factors influencing this under varying lithological conditions in the southwestern karst region. 【Method】 In this study, we selected moss-dominated biocrusts developed on dolomite and clastic rock, with undisturbed soil serving as a control. Biocrust growth characteristics were determined in situ at five levels of moss coverages (1%～20%, 20%～40%, 40%～60%, 60%～80%, 80%～100%). The soil samples, including undisturbed soil and loose soil, were collected, and scouring experiments were conducted under different hydrodynamic erosion conditions (shear force of water flow ranging from 1.68 to 12.87 Pa). Quantitative relationships between moss coverages, growth characteristics, soil properties, soil detachment capacity, and rill erodibility were established. The differences in soil resistance to water erosion under moss coverage of different lithologies were analyzed, and the main controlling factors influencing soil detachment and erosion resistance were identified. 【Result】 The results indicate that: (1) The overall thickness and biomass of mosses on dolomite were significantly lower than those on clastic rock, while the roughness was the opposite. The thickness, roughness, and biomass of mosses increased with their coverages, following either a power function or exponential growth model, and soil properties were significantly affected by both lithology and moss development (P<0.05). (2) Moss coverages significantly affected soil detachment capacity and rill erodibility (P<0.05). The rill erodibility under moss coverages on dolomite decreased by 54.57%～99.98%, and on clastic rock by 69.11%～99.93%. (3) Regression analysis revealed that soil detachment capacity and rill erodibility in dolomite mosses were controlled by water-stable aggregates and mean weight diameter, while those in clastic rock mosses were controlled by water-stable aggregates. 【Conclusion】 In conclusion, the development of biocrusts significantly improves soil erosion resistance , with variations in water-stable aggregates and mean weight diameter caused by lithology being critical factors influencing soil erosion resistance. The results provide important scientific insights for ecological restoration and biological crust-based soil erosion prediction in the southwestern karst region.