Spatial simulation is very important study field, by which we can forecast or reproduce a phenomenon in computer. Storm flow may become to flood when the channels or lakes can't hold the surface water, so it is very useful and significant to simulate the process of storm flow in computer. In past years, simulation on surface water flow has made a great progress, and many corresponding simulation models have been produced. However, those models are almost steady-state model, which just focus on the water flow result rather than process, and also they are always very complicated, inefficient or inaccurate, when Cellular Automata model has been referred to spatial simulation area, the simulation becomes easier ,and the simulation models become simple and efficient. Strom flow is one kind of surface water flow, However it has its own special characteristics. In this paper, a spatial simulation model for storm flow process based on Cellular Automata is proposed, which is an unsteady-state model (real time dynamic model).Using this model, we can simulate the entire process of the storm flow in computer rather than just the flow result. At last, for instance, the storm flow process of a small part of Jinsha river watershed has been simulated by the model. The simulation results show a good agreement with the fact.