Qiaogou watershed,located in the hilly-gullied loess region,was chosen as the study area.Based on the observed data from the natural runoff plots and hydrological stations built on different landscape positions, the temporal and spatial characteristics of sediment delivery ratios(SDR)under single rainfall events were discussed.The dominant factors affecting the SDR were determined by correlation analysis.The results show that the antecedent soil moisture content,rainfall characteristics,runoff erosivity power and sediment relative bulk density were the main factors controlling the SDR in this area.Using these dominant elements, a sediment delivery ratio formula was built by nonlinear regression analysis.