Water-use efficiency (WUE) is fundamental in understanding the coupling relationships of the water-carbon cycle of forest ecosystems. WUE is defined as the ratio of the photosynthetic uptake of CO₂ to the simultaneous transpiration loss of water vapor through the stomata. The stable carbon isotope ratio (δ¹³C) of tree-rings can be used to trace long-term, integrated effects of elevated CO₂ and climate change on WUE and tree growth, which provides insights into how naturally growing trees respond to climate change. In the mountainous area of Beijing, northern China, forest ecosystems play an important role in preventing soil erosion and water loss, regulating the climate, and maintaining ecological stability, acting as a natural ecological barrier for Beijing city. It is of great significance to study the dynamic response of WUE and its response to climate change in this area. The present study adopted dendrochronological methods and interannual δ¹³C measurements to analyze the inter-annual variation in WUE of Pinus tabulaeformis between 1952 and 2014 in the Hongmenchuan watershed, Beijing. Moreover, we analyzed the correlation between WUE and environment factors, combined with temperature and precipitation data supported by the nearest meteorological stations. The results showed that the δ¹³C values of the P. tabulaeformis tree-ring varied in a range of -23.41‰ to -27.63‰, with an average value of -25.56‰, and the δ¹³C value reduced by 0.04‰ per year. With the meteorological data provided by the weather stations of Miyun and Shangdianzi, the WUE curve showed a quadratic function trend, and changed in a range of 5.77 to 16.53, with an average value of 9.6 and decrease of 0.175. The advantage interval, where P. tabulaeformis WUE was higher than that in other years, was when the precipitation was between 550 and 600 mm, and the average annual temperature was between 11 and 11.5℃, and the water use efficiency in the early growth stage was higher than that in later stages. The lowest value (5.76) appeared in 1994, and the highest value (16.53) appeared in 1976. From 1964 to 1980, the WUE maintained at a higher level, with an average of 13. Thus, in the past decades, WUE of P. tabulaeformis in the Hongmenchuan watershed continuously decreased, similar to the carbon sequestration capacity of forest ecosystems. WUE showed an overall significant negative correlation with annual temperature (r² = -0.82, P < 0.01) and temperature of growth season (r² = 0.6952, P < 0.01), a certain but not significant correlation with precipitation. The correlation of WUE and annual temperature was stronger in the growth season, which also reflected the influence of non-growth season temperature. WUE increased slightly when temperature decreased, but declined sharply when temperature increased by 0.205 along with per 0.1℃ temperature increase. After the sudden reduction in precipitation, WUE increased temporarily and then decreased, which showed that WUE may have been conservative. This indicates that the response of WUE is more sensitive to temperature change than to precipitation. Increased temperature and decreased precipitation caused a decrease in stomatal conductance of plant leaves that affected the carbon fixation rate.