Based on the precipitation and temperature data of the 12 meteorological stations in the "Three-River Headwaters" region and the observed runoff data of Zhimenda in the Source Region of the Yangtze River, Tangnag in the source region of the Yellow River and Qamdo in the source of Lancang River during the period of 1965-2004, this paper analyses the trends of precipitation, temperature, runoff depth and carries out significance tests by means of Mann-Kendall-Sneyers sequential trend test. Makkink model was applied to calculate the potential evaporation. The runoff model driven by precipitation and potential evaporation was developed and the influence of climate change on runoff is simulated under different scenarios. Results show that during the period of 1965-2004 the temperature of the "Three-River Headwaters" region was increasing, the runoff of the three hydrological stations was decreasing. Both of them had abrupt changes in 1994, and no significant trend changes happened to the precipitation. The runoff model suggests that the precipitation exerted positive effect on the runoff depth, while the potential evaporation played a negative role. The influence of the potential evaporation on the runoff depth of the Lancang River is found to be the most; for the Yangtze River, it is less, and for the Yellow River, it is the least.
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