According to the basic principles of fractal theory and spatial scale effect

Cesium- 137 isotope tracer technique was used to measure annually averaged soil erosion modulus of small watershed in the hilly area wit h pu rple soil in Cent ral Sichuan Province.Moreover

annually averaged deposition modulus of differ- ent small watersheds was investigated.The relation of sediment delivery ratio to rainwater collection area of small watershed was discussed.The statistical model of the relation between sediment delivery ratio and spa- tial scale effect !If small watershed was constructed.The model can be used to estimate sediment delivery ra- tio and sediment yield of small data-lacked watershed in the hilly area with pu rple soil.