Vegetation restoration typically aims to control and restore collapsing gullies, which are prevalently and seriously eroded areas in South China. However, its effectiveness has rarely been evaluated, especially on steep colluvial deposits and during the prevalent high-intensity precipitation events. The effects of Melinis minutifora and Chrysopogon zizanioides on slope erosion, and the contributions of canopy, biocrusts, and roots were investigated in this study via rainfall simulation experiments. M. minutifora and C. zizanioides effectively reduced soil sediment yield rate (SR) on steep colluvial deposits by 98.1% and 86.6%, respectively. Overall, lower and denser canopies and greater fine root volumes indicated better performance of M. minutifora compared to C. zizanioides. Canopies of both plants exerted the strongest effects and contribution rates for reducing the SR and apparent interrill erodibility, while the effects and contribution rates of biocrusts were slightly higher than those of roots on average. These results highlight the importance of low plant canopies, fine roots, and the protection of biocrusts toward the reduction of rainfall erosion. The results add to the optimization of soil conservation and management practices for steep colluvial deposits.