Abstract: The Northwest Hebei Province is located in the arid-humid transition zone in northern China. The ecosystem is highly sensitive to precipitation. Clarifying the spatial and temporal distribution patterns of precipitation and its sources can provide scientific and technological support for regional agricultural development and the efficient utilization of water resources. However, at present, the understanding of the stable isotopes of hydrogen and oxygen in precipitation is still very limited. In this study, based on the precipitation isotope observation data from three stations of Qiaodong, Zhangbei and Kangbao of Zhangjiakou City in the Northwest Hebei Province, we analyzed the temporal and spatial distribution patterns of δ²H, δ¹⁸O, and D-excess isotopes in precipitation and their environmental effects by using mathematical and statistical methods. Moreover, the water vapor sources in this region were quantitatively analyzed through the backward trajectory tracking method based on Meteoinfo software. The results revealed that δ²H and δ¹⁸O isotopes of precipitation in the Northwest Hebei Province were characterized by obvious seasonal variations, with enriched in summer and depleted in winter. The highest and lowest values of δ²H and δ¹⁸O were recorded in June and December, and the highest values were −38.7‰ and −5.7‰, and the lowest values were −164.8‰ and −21.2‰, respectively. Moreover, there was a clear temperature and latitude effect. Spatially, isotope values were depleted but with more variability with increasing latitude, i.e. from Qiaodong, Zhangbei to Kangbao. The sensitivity of precipitation isotopes to temperature increased with the rise of latitude, presenting a significant temperature effect. The local meteoric water line (LMWL) was δ²H=7.957δ¹⁸O+7.226 (R²=0.9626). The intercept was lower than that of the global atmospheric precipitation line and increased progressively from Qiaodong (4.884) and Zhangbei (7.842) to Kangbao (8.205), indicating an unobvious characteristic of water vapor evaporation. The results of backward trajectory analysis showed that the sources of water vapor at various stations in the Northwest Hebei Province exhibited similarities. During summer, water vapor from precipitation was mainly influenced by the East Asian monsoon circulation, with vapor contribution rates at Qiaodong, Zhangbei, and Kangbao were 53.53%, 55.43%, and 52.17%, respectively. In other seasons, water vapor was predominantly controlled by the westerly wind belt and Mongolian continental air masses, with contributions exceeding 70%. Notable variations occurred in transport pathway of water vapor, in spring, water vapor primarily derived from northern and western pathways, though the water vapor in Qiaodong District was additionally affected by the southerly flows from the western Pacific Ocean and the South China Sea, accounting for 25.27%. Moreover, in autumn and winter, water vapor predominantly originated from western pathways, controlled by a single westerly air mass, with proportions exceeding 90%. This study contributed to an in-depth understanding of regional water vapor cycling processes.