Abstract: 【Objective】The Heiyingshan region, located in Ejina, Inner Mongolia, is characterized by an extremely arid climate and predominantly saline groundwater. This acute water scarcity poses substantial challenges to regional socio-economic development and ecological sustainability. 【Methods】To better understand the groundwater circulation mechanisms in this region, a multi-faceted approach was employed, incorporating hydrochemical analysis, deuterium-oxygen isotopes, tritium isotopes, and carbon isotopes. The study delved into the hydrochemical properties, recharge origins, and residence durations of various groundwater types, while also assessing the impact of geological formations and ancient depositional environments on groundwater circulation. 【Results】The findings reveal that atmospheric precipitation is scarce, and intense evaporation leads to high total dissolved solids (TDS) in groundwater. The groundwater circulation model consists of three distinct stages. In the precipitation-infiltration stage, which occurs primarily in the bedrock mountain areas, groundwater receives limited recharge from atmospheric precipitation. The average turnover coefficient is 0.84%/a, and the average TDS value is 7.8 g/L. Significant variation in groundwater age is observed due to the heterogeneity of the aquifer media. The leaching-accumulation stage occurs within the piedmont alluvial fan system. This stage is characterized by a progressive decrease in the groundwater refreshing rate from the fan apex towards the distal fringe, concomitant with salt enrichment driven by evaporative concentration. The average total dissolved solids of groundwater in this stage is 9.0 g/L. The subsequent convergence-evaporation stage is situated in the major basin areas where the aquifer system receives lateral inflow from the bedrock mountainous regions supplemented by minor contemporary precipitation. This stage exhibits an elevated average total dissolved solids of 9.8 g/L and a mean refreshing rate of 0.59%/a. The confined groundwater in this terminal stage yields a mean residence time of approximately 17 thousand year.【Conclusion】The evolution of groundwater in the Heiyingshan region is the result of the interplay of paleoenvironmental and modern water cycle processes. Atmospheric precipitation recharge from cold and humid paleoenvironments mixed with modern water, and ultimately formed brackish and saline waters through evaporation and concentration in the basin area. In some regions, paleowater with low total dissolved solids is preserved. This study offers a scientific foundation for pinpointing areas with freshwater potential and elucidating the origins of saline groundwater in extremely arid regions.