Biocrusts are extensive surface covers in drylands and play a vital role in the hydrological processes. Although the impacts of biocrusts on runoff volume were extensively studied, their influence on runoff processes, particularly at patch scale, remains poorly understood. To fill this knowledge gap, we measured the functional traits affecting hydrological processes of biocrusts at five succession stages, and explored the influence of these traits on the wetted perimeter of the cross-section, which is the major factor affecting runoff resistance. A simulated runoff experiment with flow rate of 1.5 mm center dot min- 1 was conducted to study the effect of these traits on the runoff process at patch scale of 30 cm x 20 cm. Our results showed a marked increase in biocrust functional traits, such as shoot height, leaf density, and biomass, as they progressed through successional stages. This increase subsequently led to a significant increase in the wetted perimeter of cross-section. Biocrusts with moss coverage above 95 % had a wetted perimeter of 213.33 mm center dot cm- 1, which was 20.4 times greater than that of biocrusts with moss coverage below 5 %. With increasing wetted perimeter, runoff velocity decreased logarithmically, ranging from 0.2244 m center dot s-1 to 0.0217 m center dot s-1. Conversely, runoff resistance increased exponentially, ranging from 0.05 to 53.04. Furthermore, runoff coefficient declined as the wetted perimeter increased. Biocrust biomass (B) was the most important factor affecting the wetted perimeter (chi), as evidenced by a strong positive correlation (chi = 0.4083B + 0.5047, R2 = 0.9957). Increases in biocrust biomass increased the wetted perimeter, which in turn reduced runoff velocity, enhanced runoff resistance, and decreased runoff coefficient. This study provided new insights into the role of biocrust patch in shaping runoff processes and highlighted the contribution of biocrust functional traits to dryland hydrological processes.