Abstract: Water and sediment modeling is one of the most important tools for calculating and evaluating soil erosion and sediment erosion. The Loess Plateau is one of the most serious areas of soil erosion in China. A water and sediment model for small watersheds in Loess Plateau based on physical mechanism is developed by coupling the rainfall-runoff, soil erosion and sediment transport module. The rainfall-runoff module is Tank model, the soil erosion module includes rainfall splash erosion, loess slope erosion, gully slope erosion and groove erosion, and the sediment transport module uses the combined method of sediment balance equation and storage and discharge equation. Chabagou catchment in Loess Hilly and gully region of Wuding River, a tributary of the Yellow River, is taken as the study area, and the simulation results are compared with MUSLE (Modified Universal Soil Loss Equation) model to explore the influence of different water and sediment models on the simulation results. The results show that: (1) the developed model takes into account the characteristics of the erosion process of the Loess Plateau in detail, which makes the physical mechanism clearer and the erosion calculation more comprehensive. (2) the developed model has higher accuracy and reliability than the model based on the empirical MUSLE. The average NSE is 0.722, and the average of absolute value of relative error of sediment load is 21.3%, while the average NSE of the MUSLE model is 0.576, and the average of absolute value of relative error of sediment load is 32.8%. The results can provide a better understanding and modeling of the sediment processes and water and soil erosion control of Loess Plateau.