Knowledge of past climatic variability in the eastern Tianshan Mountains of arid Central Asia is still limited due to the lack of long-term instrumental data. In this study, we develop a March–August mean temperature reconstruction since 1766 ce based on annual tree-ring widths of Schrenk spruce (Picea schrenkiana Fisch. et Mey.). The reconstruction accounts for 51.8% of the temperature variation during the calibration period (1957–2017). Over the last two and a half centuries, the region has experienced six warm periods, namely 1766–1792, 1803–1827, 1878–1886, 1904–1916, 1926–1935, and 1982–2015. The reconstruction also indicates the occurrence of two significant cold periods, 1821–1857 and 1931–1980. Over the past 252 years, the climate in this region has shifted between warm-dry and cold-wet periods. However, a strong warm-wet trend since the 1980s is evident. There is a strong positive correlation between the tree-ring temperature reconstruction and the North Atlantic Oscillation, as well as a close relationship with strong volcanic eruptions in the mid-high latitudes.