Abstract: The source area of Yangtze River（SAYAR） and the source area of the Yellow River（SAYER） are located in the hinterland of the Qinghai-Tibet Plateau, which are sensitive areas for global climate change. Different runoff components in these regions are strongly affected by climate change, and changes in runoff components, especially high flow, may cause a series of impacts on the ecology and human production activities. To investigate the characteristics and the reasons of different runoff components for their changes, relevant studies are conducted based on multi-year runoff and meteorological data of SAYAR and SAYER with the methods such as flow duration curve（FDC）, MannKendall（M-K） method and multiple linear regression. The results show that:（1）The high flow（Q10～Q30）, medium flow（Q40～Q60） and low flow（Q70～Q90） in SAYAR increases at the rates of 4.68, 2.18 and 0.38 m3/（s·a）, respectively, during 1964-2021; the high flow and total discharge in SAYER had the same trend during 1962-2021, decreasing at the rate of 1.99 and 0.16 m3/（s·a） respectively, but the medium flow and low flow increased at rates of 0.12 and 0.68 m3/（s·a）, respectively.（2） During the period from 1979 to 2018, the increase in precipitation was the main reason for the increase in high flow and medium flow in SAYAR, and its contribution rate to the change of high flow and medium flow was 92.93% and 71.17%, respectively. The temperature rise was the main reason for the increase in low flow in SAYAR, and its contribution rate to the change of low flow was 77.72%.（3） During the period from 1979 to 2018, the increase in temperature was the main reason for the reduction of high flow and medium flow in SAYER, and its contribution to the change of high flow and medium flow was-58.79% and-53.98%, respectively. The increase in precipitation was the main reason for the increase of low flow in SAYER, and its contribution rate to the low flow was 67.11%.This paper may provide some reference for water resources management and ecological environment protection in the source regions of the Yangtze River and the Yellow River under the background of climate change.