Abstract: A distributed hydrological model based on cellular automata (CA) is developed to simulate the rainfallrunoff process in small sized watersheds.The distributed model is built by extending cellular states and transformation rules,as well as the time step in the general CA model.The model consists of five substates with five cellular parameters and two transform ation rules,and is fully integrated with a geographic information system (GIS) platform.The model is validated using the observed rainfall-runoff data from the Chabagou watershed in the Loess Plateau region of the Yellow River Basin.The results show that the three evaluation indexes,the deterministic coefficient,the peak time error and the peak forecast error,all reach certain accuracy.The simulated runoff process can also be visualized on the GIS platform.The CA based distributed hydrological model shows potential efficacy of simulating event based rainfall-runoff processes in small watersheds.