Biological soil crust (BSC), as a groundcover, is widely intergrown with grass. The combined effects of BSC and grass during rainfall on runoff and sediment yield are still unclear. In this study, simulated rainfall experiments were applied to a soil flume with four different slope cover treatments, namely, bare (CK) and Stipa bungeana Train. (STBU), BSC, and STBU + BSC to observe the processes of runoff and sediment yield. Additionally, the soil moisture at different depths during infiltration was observed. The results showed that the runoff generated by rainfall for all treatments was in the following order: BSC>STBU+BSC>CK>STBU. Compared with CK, the STBU promoted infiltration, and BSC and STBU+BSC inhibited infiltration. The BSCs obviously inhibited infiltration at a depth of 8 cm. As the soil depth increased to 16 cm and 24 cm, the effects of STBU on promoting infiltration were stronger than those of BSC on inhibiting infiltration. Compared with the CK, the flow velocity for the BSC, STBU and STBU + BSC treatments was reduced by 62.79%, 32.27% and 68.29%, respectively. The BSC and STBU increased the critical shear stress by increasing the resistance. Additionally, the BSC, STBU and STBU+BSC treatments reduced the sediment yield rate by 80.8%, 99.8% and 99.9%, respectively. The soil erosion process was dominated by the soil detachment capacity in the CK, BSC and STBU+BSC treatments, while the STBU treatment showed a transport-limited process. This study provided a scientific basis for the reasonable spatial allocation of vegetation in arid and semiarid areas and provided a scientific basis for the correction of vegetation cover factors in soil erosion prediction models.