Tree-ring is one of the important indicators of environmental evolution, which can obtain the climate data of global change of the past, and this method is very accurate and has good continuity, high resolution and reconstruction precision. This paper discussed the relationship between the surface runoff and tree-ring of Populus euphratica. The trend changes of runoff in the upper-middle reaches of the Tarim River and the tree-ring width of P. euphratica were analyzed by Mann-Kendall test. Combining the tree rings and the historical documents, the response of tree-ring in the lower reaches of the Tarim River to water supply was analyzed. The results showed that: (1) For nearly about 50 years(1957-2010), the tree-ring width showed a significant decline in the upper and middle reaches of the Tarim River, and the runoff has the same change trend. The statistical value of | Zc | was higher than 0.96. (2) The tree-ring width declined from 1913 to 2000, and it was more obvious during 1973-2001 and became the lowest level during the last 100 years. The formation, river course change and flowing back into old river course of the Layihe River in the middle-lower reaches of the Tarim River were all proved in tree-rings, which recorded the same as the historical documents. (3) The development of ecological water conveyance project improved the ecological environment in lower reaches of the Tarim River, which can be verified from the tree-ring. The treering width after 2000 never reached a high level as before 1920, which showed that the current ecological water is limited to the desert riparian forest recovery. (4) For response of tree-ring of P. euphratic to water supply, the wavelet analysis method and historical documents drew the same conclusion.