Biological soil crusts (biocrusts) play a pivotal role in mitigating soil erosion and should be included in the covermanagement factor (C-factor) for improving the accuracy of soil erosion models. The study aimed to quantify the influence of biocrusts development on soil erosion and to establish a biocrusts factor (Bbc) for integration into the C-factor calculation. This was achieved through indoor simulated rainfall experiments, complemented by two years of field monitoring, to evaluate the mechanism of biocrusts on soil erosion and refine the Bbc. The biomass (chlorophyll alpha, mu g center dot g(-1)) was used as an indicator to evaluate the development of biocrusts. Results indicated that: (1) The biocrusts development significantly increased the cohesive force and thickness, while simultaneously reducing the saturated hydraulic conductivity. (2) Biocrusts development led to a substantial reduction in erosive potential, which could be attributed to increase of biocrusts thickness. (3) Biocrusts development showed clear thresholds in its effect on soil erosion: erosion was effectively controlled above 9 mu g center dot g(-1), but became unstable below 1 mu g center dot g(-1). (4) The Bbc was represented by a piecewise function: the value was set to 1 for biomass < 1 g center dot g(-1), 0.01 for biomass > 9 mu g center dot g(-1), and an exponential function was employed for biomass between 1 and 9 mu g center dot g(-1). The Nash values for the validity of biocrusts factor were 0.82 and 0.66, and the RMSE values were 0.10 and 0.08, respectively. By integrating biocrusts into the C-factor calculation of soil erosion models, this study significantly enhanced prediction precision.