Abstract: Northwest Hebei Province is located in the arid-humid transition zone in northern China, where 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 precipitation isotope observation data from three stations located at Qiaodong, Zhangbei, and Kangbao in Zhangjiakou City, Northwest Hebei Province, we analyzed the spatial and temporal distribution patterns of δ²H and δ¹⁸O isotopes and deuterium surplus (D-excess) in precipitation and their environmental effects using mathematical and statistical methods. Moreover, the water vapor sources in this region were quantitatively analyzed using the backward trajectory tracking method based on the MeteoInfo software. Results revealed that the δ²H and δ¹⁸O isotopes in precipitation in Northwest Hebei Province were characterized by obvious seasonal variations, exhibiting enrichment in summer and depletion in winter. The highest and lowest values of both δ²H and δ¹⁸O were recorded in June and January, respectively. For δ²H and δ¹⁸O, the highest values were −38.7‰ and −5.7‰, and the lowest values were −164.8‰ and −21.2‰, respectively. Moreover, the isotopes in precipitation had clear effects of temperature and latitude, but no significant precipitation effect. Spatially, isotope values were depleted albeit with increased latitude, following the order of Qiaodong > Zhangbei > Kangbao. The sensitivity of precipitation isotopes to temperature increased with increasing latitude, indicating a significant temperature effect. The local meteoric water line (LMWL) was δ²H = 7.957δ¹⁸O + 7.226 (R² = 0.962). The slope was closed to and the intercept was lower than those of the global meteoric water line, indicating a nonobvious characteristic of water vapor evaporation. The intercepts increased progressively from Qiaodong (4.884) to Zhangbei (7.842) and Kangbao (8.205). The results of the backward trajectory analysis showed that the sources of water vapor at the three stations in Northwest Hebei Province exhibited similarities. During summer, water vapor from precipitation was influenced mainly by the East Asian monsoon circulation, with the vapor contribution rates at Qiaodong, Zhangbei, and Kangbao being 53.53%, 55.43%, and 52.17%, respectively. In other seasons, water vapor was controlled predominantly by the westerly wind belt and Mongolian continental air masses, with their combined contribution exceeding 70% of the total.Notable variations occurred in the transport pathway of water vapor: in spring, water vapor was derived primarily from northern and western pathways, although the water vapor in Qiaodong was affected also by southerly flows from the western Pacific Ocean and the South China Sea, accounting for 25.27% of the total; in autumn and winter, water vapor originated predominantly from western pathways, while being controlled by a single westerly air mass, with proportions exceeding 90% of the total. Overall, this study contributes to an in-depth understanding of regional water vapor cycling processes.