The soil crust on slope farmland is a sort of compact slab structure formed by rainfall on the soil surface, and it has the characteristics of being smooth, compact, and easy to become ramous. Previous researchers have done a multitude of experiments regarding development mechanism, process of formation and factors affecting them, and their findings indicated that the soil crust has effects in decreasing infiltration, improving soil surface runoff amount, influencing the process of sediment yield, and reducing the biomass and yield of crop and so forth. Protecting slope farmland against soil and water loss has become an important issue of constructing bio-environment and realizing sustainable development in China. It is evident that the soil crust is a special underlying surface and it has significant effect on runoff amount and sediment yield on the slope. Planting is the main activity on slope farmland, and it has certain influence on the soil crust. The objectives of this study were to investigate the effects of soil crust on runoff and sediment yield under soybean cover and to provide theoretical basis for soil and water conservation and rational utilization of slope lands. Our study was carried out in the southern fringe of the Loess Plateau in 2010. Soil in the study area is Eum-Orthic Anthrosols. The intensity of the precipitation in this research was 80 mm/ h, with each rainfall lasting for 60 min. We took slopes planted with soybean as object, and by using simulated rainfalls we investigated the existence of soil crust before rain and influences of its thickness and coverage on runoff and sediment yield. Soil crust before rain had considerable effects on runoff and sediment yield. Analysis of the effects of soil crust on runoff and sediment yield on slope land under soybean cover showed that, the volume of runoff was higher on soil crusted slopes and amount of soil loss was much lower compared to that on slopes without soil crust. The soil crust made the beginning time of runoff yield earlier. With the growth of the soybean, the beginning time of runoff yield on the slope without crust was postponed much. The runoff and sediment yield became lower on slope land with soybean growing, and the soil crust on slope made the surface smoother. Besides, the structure of the soil crust is compact, which speeds up the runoff, lower the infiltration of rainfall and runoff, and keeps the runoff amount on slope with prophase soil crust at a relatively high level. On bare soil, the runoff and sediment yield on soil crusted slopes was 5.27% higher and 27.66% lower than that on slopes without soil crust, respectively. On slopes with soybean cover, the runoff and sediment yield on soil crusted slopes was 24.81% higher and 14.26% lower than that on slopes without soil crust, respectively. The crust has great influence on the processes of the runoff and sediment yield, which have significant difference between the slope with prophase soil crust and without soil crust. On the whole, the fluctuation of the process of runoff and sediment yield was smooth on slope with prophase soil crust, while the volatility of slope without soil crust fluctuates greatly. The presence of soybean cover increased the difference in runoff yield between slopes with and without soil crust, but reduced the difference in sediment yield. The effect of soybean on the differences of runoff and sediment yield between slopes with and without soil crust became stronger with the growth of soybean plants. Effects of thickness and coverage of soil crust on runoff and sediment yield were not significant. The influence of soil crust on the soil erosion varied greatly due to different soil types, terrain, rainfall, crops and other factors, which makes the problem become more complex. The research on the principle of the influence of soil crust on soil erosion is helpful for illustrating the progress of such effects, which provides reference for agricultural sectors to weigh the pros and cons in the real production.