Water security in arid regions has become a critical challenge under ongoing global environmental change. Using arid Xinjiang as a case study, this research reconstructs the spatiotemporal evolution of hydrographic network density (HND) over the past 120 years (1900-2020s) based on historical maps and GIS-based spatial analysis. A grid-based HND dataset was developed for five representative periods to examine long-term structural changes in regional water systems. The results reveal a clear transition from early spatial dispersion to post-mid-20th-century aggregation and subsequent stabilization, with the 1960s marking a key turning point in hydrographic network organization. Spatial autocorrelation increased steadily over time, indicating the emergence of increasingly structured and clustered water systems. Climatic aridity factors-particularly the Palmer Drought Severity Index (PDSI)-exerted dominant controls on hydrographic dynamics in mountainous regions, whereas changes in oasis-plain systems were increasingly driven by human activities, including cropland expansion, irrigation development, and policy-led water management since the mid-20th century. By integrating long-term historical cartographic data with quantitative spatial analysis, this study provides new empirical evidence on how climate forcing and human engineering have jointly shaped water-system evolution in arid environments. The findings offer a long-term perspective for understanding human-environment interactions and for informing water-resource management and adaptation strategies in arid regions under future climate change.