Climate change and human activities are the two main factors that affect the hydrological processes and water resources in a catchment. The objective of the study is to distinguish the contribution of climate change and human activities on the variation of runoff in the Dongting Lake catchment. The daily hydro-climatic data from 19852010 were analyzed with the accumulated anomaly analysis method and the non-parametric Mann-Kendall test. The contribution of climate change and human activities on the change of runoff were calculated by the quantitative method. The whole period was divided into two sub-periods according to the breakpoint(period 1:before the breakpoint; period 2:after the breakpoint). Compared to period 1, the runoff at the whole Dongting Lake catchment decreased by 28 mm with the four sub-catchments of Xiangjiang, Zishui, Yuanjiang and Lishui decreased by 15 mm, 130 mm, 112 mm and 102 mm respectively during period 2. The decrease of annual precipitation and the increase of annual potential evapotranspiration may account for the runoff change. Results showed that climate change was the main contributor for the decrease of runoff, accounting for 64% of the runoff change. The overall impacts of human activities and climate change may result in a decrease of catchment runoff despite of the potential increase of runoff caused by human activities. The study implies that the hydrological drought in the Dongting Lake catchment was mainly influenced by the natural factor such as climate change.