Tianshan Mountains are an important area for water source ; they are dominated by westerly winds and play an important role in global climate change research. It is vital to understand past precipitation changes and explore their mechanism for the current sustainable utilization of regional water resources. Since the Tianshan Mountains are located in an arid inland area, tree rings are sensitive to climatic moisture status and are a good proxy of past precipitation. In this study, we developed a tree-ring-width chronology of Schrenk spruce (Picea schrenkiana Fisch. et Mey) in the Sayram Lake Basin of the Tianshan Mountians. Climate-growth response results showed that the precipitation from the previous August to current July was the principal limiting factor of radial growth. We also obtained a 373 a reconstruction of August-July precipitation in the Sayram Lake Basin. The reconstruction explained 39.8% of the variance in precipitation records during the 19602009 calibration periods. Additionally, the precipitation over the past 373 a in the Sayram Lake Basin has experienced six drier and seven wetter periods, and the extreme drought years were 1714, 1775, 1847 and 1917; 1917 was the driest year in the past 373 year, and the driest decade was the 1910s. Meanwhile, there was large power in the 11 12 a, 3.0 a,2.5 a, 2.1 a and 2.0 a periods. We suggest that the precipitation variability could be associated with large-scale oscillations in the climate system. The reconstruction illuminates precipitation variability and changes in a region where the climate history over the past several centuries is poorly understood.