Based on high resolution dynamic downscaling meteorological forcing data, climate change of Tibetan Plateau and possible trends in runoff of the source region of Yangtze River and Yellow River were analyzed by using large-scale distributed hydrology model under future climate warming. The average annual runoff of the source region of Yangtze River and Yellow River will increase by 8.58% and 9.19% in the future 30 to 50 years. Although the annual precipitation will increase up to 4.48%, the average annual runoff of the source of Yellow River will reduce only by 1.98% in the next 30 to 50 years. The variations of runoff in the source area of Yangtze River and Yellow River are analyzed by using the climate data projected for the future 30 to 50 years and the scenario simulations of the land use/cover change. These results indicate that the runoff is the minimum (maximum) at forest land (bare land).