Abstract: In order to study the evolution law of runoff in the source region of Changjiang River, the WEP-QTP(the Water and Energy transfer Processes in the Qinghai-Tibet Plateau) model was used to simulate the water cycle process in the source region of the Changjiang River from 1956 to 2020,and the driving mechanism of runoff change was quantitatively analyzed based on the multi-factor attribution analysis method.The results showed that from 1956 to 2020,the proportions of rainfall runoff, snowmelt runoff and glacier melt runoff in the runoff components in the source region of the Changjiang River were 79.4%,17.2% and 3.4%,respectively.Comparing the base period(1956～1998) and the change period(1999～2020),the runoff variation under the influence of climate was 2.14 billion m3,and the contribution rates of temperature and precipitation to the increase of runoff were-8.4% and 108.4%,respectively.Analysis of runoff components showed that the rainfall runoff variation under the influence of climate was 2.48 billion m3,and the contribution rates of temperature and precipitation to the increase of rainfall runoff were 36.2% and 63.8%,respectively.The snowmelt runoff variation under the influence of climate was-310 million m3,and the contribution rates of temperature and precipitation to the decrease of snowmelt runoff were 348.1% and-248.1%,respectively.The glacier melt runoff variation under the influence of climate was-30 million m3,and the contribution rates of temperature and precipitation to the decrease of glacier melt runoff were-21.5% and 121.5%,respectively.The monthly process of runoff and its components was analyzed, and the impact of climate change on runoff and its components was mainly concentrated from June to October.