Abstract: Geomorphy is one of the key factors that affect soil erosion in Watershed. For further study on the relationship between geomorphic development and erosion sediment yield, the process of geomorphic development and the variation of sediment yield were studied with generalized small watershed model by simulated rainfall experiment, high-precision photogrammetry and GIS technique. The results showed that the speed of sediment yield (Gt), sediment yield intensity of rainfall (Gp) and average sediment transport intensity (M) had a tendency of increase at the beginning and then decrease along with the process of geomorphic development. Variation trends of Gp and M turned from increase to decrease at critical ground fracture degree (about 32%) and critical relative watershed volume (about 65%). This critical phenomenon is very important for studying geomorphic development and sediment yield in depth. It also showed that ground fracture degree and relative watershed volume could be considered as one index of watershed development degree.