[Objective] Studying the processes and driving factors of runoff and sediment in a typical watershed in the upper reaches of Ganjiang River, to provide bases for soil erosion control, land use and function adjustment in this area.[Methods] Daily runoff, sediment and precipitation data from 1980-2015 were used in this study. The characteristics and relationships between precipitation, runoff and sediment yield were analyzed by using Mann-Kendall method, hydrological method and double mass curve, from this the driving factors of runoff and sediment yield changes were determined.[Results] ① There was a significant decrease in sediment yield, while an abrupt change appeared in 2005. From 2003, the runoff yield also showed a decreasing but not apparent trend. ② Runoff and sediment yield were different in term of the beginning time of the abrupt change. The change of runoff was divided into two phases, which were from 1980 to 2002 and from 2003 to 2015, while the sediment yield had two change phases of 1980-2004 and 2005-2015. ③ The decrease value of annual average runoff during 2003-2015 was 7.26×10¹⁰ m³. The decrease value of average annual sediment yield during the period of 2005-2015 was 8.82×10⁷ t. ④ The runoff reduction volume caused by human activities was 5.77×10¹⁰ m³/a, accounting for 76.8% of the total; the sediment decrease was 8.44×10⁷ t/a, accounting for 95.7% of the total sediment yield.[Conclusion] Runoff and sediment yield were all reduced, and the amount of sediment yield was reduced significantly. Either for runoff reduction or for sediment discharge, the ratios caused by precipitation and human activities was about 4:1.