Abstract: Hydrogen and oxygen isotope data from atmospheric precipitation were collected and analyzed at six stations located on both the northern and southern sides of the Qinling Mountains. Based on this analysis， the precipitation isotope lines， environmental effects， d-excess （deuterium excess） characteristics， and differences in water vapor sources between the two regions were elucidated. The following results were obtained： （1） The slope of the meteoric water line equation in the northern foot of the Qinling Mountains （7.84） was greater than that in the southern foot （7.52）， which in turn was greater than that in the eastern monsoon region （7.46）. For the intercept， the southern foot of the Qinling Mountains （13.10） was higher than the northern foot （10.10）. （2） A temperature effect was identified on the northern slope during the cold season， while a strong precipitation amount effect was demonstrated on the southern slope. Significant latitude effects were exhibited on both sides， with depletion gradients that far exceeded the national average. （3） During summer， precipitation on the northern slope was determined to originate from low-latitude oceanic regions with high relative humidity， resulting in a d‑excess lower than the annual average. In winter， precipitation was derived from westerly circulation carrying North Atlantic water vapor with lower relative humidity， leading to a higher d‑excess. These findings provided important theoretical insights into the Qinling Mountains’ role as the “Central Water Tower” and offered scientific support for water resource management on both sides of the mountain range.