Due to the spatial and temporal variations of environmental factors, the processes of soil erosion and sediment yield in medium and large watersheds are much more complex than those in small watersheds. As a result, both empirical and physics-based models can hardly be applied in medium and large watershed with a reasonable result. This paper first illustrates the characteristics of soil erosion and sediment yield in the medium and large watersheds, and then gives a review of the models developed for the watersheds. Some methodologies to upscaling, which may be an important approach to simulating the processes of soil erosion and sediment yield in the medium and large watershed, are also discussed.