The Tianshan Mountains serve as a crucial water resource formation zone in China"s arid northwest region. Understanding the hydrological processes within this area holds significant implications for water resource management in arid zones. The northern slope of the Tianshan Mountains lies at the heart of the Eurasian continent, encompassing primarily the region north of the Tianshan range and the southern edge of the Junggar Basin. It exhibits a typical temperate continental climate. While previous studies have primarily focused on precipitation and groundwater isotopes in arid regions, systematic investigations of river water hydrogen and oxygen stable isotopes across the entire northern slope of the Tianshan Mountains remain scarce. To reveal the stable isotope characteristics of river water on the northern slope of the Tianshan Mountains in the arid northwest region and their implications for the hydrological cycle, this study systematically collected river water samples from major rivers on the northern slope of the Tianshan Mountains between 2022 and 2025. Based on hydrogen and oxygen stable isotope data from 225 samples, it combined isotope analysis with remote sensing technology to elucidate the spatiotemporal variation characteristics of hydrogen and oxygen stable isotope compositions in river water. The study also analyzed the influence of river water physicochemical properties and environmental factors on these isotope compositions. The results indicate:(1) River water hydrogen and oxygen stable isotope compositions exhibit distinct spatiotemporal variation patterns. The ranges of δ²H and δ1?O values for rivers on the northern slope of the Tianshan Mountains were ?117.2‰ to ?46.4‰ and ?17.84‰ to?7.10‰, respectively, with regional averages of ?78.3‰ and ?13.27‰. The temporal variability in the stable hydrogen and oxygen isotope composition is relatively small. Spatially, significant regional differentiation is evident: the western, central, and eastern regions exhibit average δ2^{H and δ}18^{O values of} ?85.8‰,?14.16‰ and ?71.0‰,?12.28‰ and ?81.0‰, ?13.74‰, respectively, forming a spatial distribution pattern with higher values in the central area and lower values in the eastern and western wings.(2) The regional river water line (EL) equation is δ2H = 4.31δ18^{O? 21.94 (}R2=0.72, n=225), with a slope (4.31) significantly lower than that of the local atmospheric precipitation line (slope 7.51) and the global atmospheric precipitation line (slope 8); The hydrogen and oxygen stable isotope compositions of rivers in the western and central regions are primarily dominated by precipitation recharge, while eastern rivers exhibit a strong signal of evaporative fractionation.(3) Hydrogen and oxygen stable isotope compositions in rivers on the northern slope of the Tianshan Mountains are influenced by multiple factors. The physicochemical properties of the river water itself contribute to its isotopic characteristics. Additionally, environmental factors such as precipitation, evapotranspiration, surface temperature, and vegetation cover influence river isotope compositions by regulating local hydrological processes. This study elucidates the spatiotemporal variation patterns of stable hydrogen and oxygen isotopes in river water along the northern slope of the Tianshan Mountains. Through field sampling and remote sensing techniques, it quantitatively identifies the primary factors influencing the stable hydrogen and oxygen isotope composition of regional river water. This research fills a gap in studies using stable hydrogen and oxygen isotopes in river water to indicate hydrological processes across the entire mountain range scale of the northern Tianshan slope, providing isotopic evidence for a deeper understanding of water cycle processes in the Tianshan region"s watersheds.