In recent years,due to the dual impacts of climate change and human activities,the annual runoff of the Chongqing section of the upper reaches of the Yangtze River decreased significantly. In this paper,the MASH moving average method was used to analyze the runoff variation characteristics at three main hydrological stations in Chongqing : Cuntan,Beibei and Wulong. Further,the elastic coefficient method,together with the regression analysis method was adopted for runoff simulation,in an attempt to evaluate quantitatively the contribution rates of climate change and human activities on runoff change. The results showed that: ( 1)the contribution rates of climate change and human activities to the annual runoff reduction at all three hydrological stations were about 25. 2%~ 35. 2% and 64. 8% ~ 74. 8%,respectively for the period of 1991 - 2011,compared to the reference period of 1961-1990. ( 2)The impact of climate change on monthly runoff is limited. Consequently,runoff in July increased to a certain extent,and runoff in August to October generally reduced. The influence of human activity was obvious,leading to a slight increase in runoff from December to April and runoff reduction from May to November. ( 3)Both methods indicated that human activities were the major factor causing runoff reduction. Quantitative assessment of the causes of runoff changes helps formulate scientific countermeasures and coordinate the development and utilization of water resources in the upper reaches of Yangtze river.