This paper takes Hemingguan watershed and Lizikou watershed in Nanbu County,Sichuan Province as study areas and discusses the sediment delivery ratio(SDR) based on the distributed models of soil erosion and sediment yield from the two watersheds.Results show that the main factors affecting the SDR are different in the two watersheds.Rainfall amount and runoff volume are main factors in Hemingguan watershed but in Lizikou watershed,the main factors are runoff volume and rainfall intensity.The reason is that the size of Hemingguan watershed is much smaller than Lizikou watershed.Moreover,there is a tendency that the SDR for single rainfall gets smaller as the size of study area increases.Finally,the paper analyzes the relations of the SDR to rainfall amount,antecedent soil moisture,and runoff coefficient and constructs two formulas of SDR for the two watersheds.