Through the analysis of nearly 50 year annual runoff data of Tarim River,the evolution trend of runoff under changing environment is investigated. Possible impacts on the runoff process are discussed in the two aspects of climate change and human activities. Results show that under changing environment,the runoff process of Tarim River in nearly 50 years has been significantly changed. Under the influence of climate change characterized by temperature rising and precipitation increasing,runoff in headstream zone of Tarim River generally has an obvious increasing tendency. Temperature variation has little effect on regional evapotranspiration,but increases glacial meltwater runoff. There are some differences in the effect of precipitation increasing runoff among different headstream zones of Tarim River. However,human activities are the dominant influencing factor to runoff changes. The construction of hydraulic engineering and the increased amount of water use have significantly changed the runoff process of Tarim River and comprehensive management engineering of Tarim River has positive effects on the whole basin.