Biocrusts affect soil detachment through above-ground (top crust's surface covering) and below-ground (sub-crust's binding and bonding, B&B) effects, which might vary with biocrust development or coverage. However, these effects in humid climates are still unclear. This study was conducted to apportion and quantify the surface covering and B&B effects of moss biocrusts with five coverage levels (1%-20%, 20%-40%, 40%-60%, 60%-80%, and 80%-100%) on soil detachment by overland flow in a subtropical humid climate. Two treatments with one being intact moss crusts and one removing the above-ground moss tissues were designed for each coverage level, and bare soil was used as the baseline. The results indicated that soil detachment capacity (D-c) and rill erodibility (K-r) decreased with biocrust coverage. After removing the above-ground moss tissues, the impeding effect of biocrusts on soil detachment weakened, but still increasing soil erosion resistance relative to bare soil. For intact crust, D-c was reduced by 50%-95% compared with bare soil, wherein 36%-55% and 14%-40% were attributed to the surface covering and B&B, respectively. The top crust contributed more than sub-crust to the soil detachment reduction, which were related to but not linear with biocrust coverage. When biocrust coverage reached mid-to-higher level (40%-100%), both top crust and sub-crust steadily contributed to soil detachment reduction with 60% and 40%, respectively. The findings advance a better understanding of the influencing mechanism of biocrusts on soil erosion in humid climates and highlight the importance of saving biocrusts as ecosystem functions.