It is very important to dynamically simulate and forecast the development and evolution of soil erosion processes.The traditional soil erosion model is a steady-state model,which is not good at dynamically simulating the initiation and development of soil erosion processes.Cellular automata(CA) is a "from down to up" dynamic modeling framework,being capable to simulate the spatial-temporal evolutionary process of a complex geographical system.A basic thought that CA is applied to simulate soil erosion processes is put forward using theory and method of CA.By taking the loess hill and gully region as an example,a process model of soil erosion in small watershed based on CA is constructed.