A watershed model was established based on a field survey of a small watershed located in the Three Gorges Reservoir region, three simulated rainfall events which intensities were 60, 90 and 120 mm/h on the watershed to study the process of runoff and sediment yield. The results showed that the runoff and sediment yield increased with the increase of rainfall intensity, but the runoff yield increased much faster than sediment yield. In each of the three rainfalls, the runoff showed the tendency of increasing initially before tending to be stable, but the sediment yield changed quite complicated. In each rainfall, both the cumulative runoff and sediment yield varied in a linear function law with the increase of rainfall duration. A fluctuation change of sediment concentration was showed in three simulated rainfalls experiments.