Abstract: 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. 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. The findings reveal that atmospheric precipitation is scarce, and intense evaporation leads to high total dissolved solids (TDS) in groundwater. The groundwater circulation patterns in this region can be broadly categorized into three types. In the basins, groundwater circulation follows a convergence-evaporation model, which represents a blend of ancient precipitation from cold and humid paleoclimates and modern water, receiving lateral runoff from bedrock mountains and minimal atmospheric precipitation. This results in an average TDS of 9.8 g/L and an average turnover coefficient of 0.59%/a. The confined groundwater in this area has an average age of 17,000 years. In some basin sections, groundwater with relatively low TDS is observed. In alluvial fans, the groundwater circulation adheres to a dissolution-accumulation model, with the turnover coefficient decreasing from the fan apex to the fan margin. Evaporation leads to salt accumulation, resulting in an average TDS of 9.0 g/L. In the bedrock mountains, the circulation pattern is primarily driven by precipitation-infiltration, albeit with limited recharge. Groundwater exhibits an average turnover coefficient of 0.82%/a and an average TDS of 7.8g/L. The heterogeneity of the aquifer media results in substantial variations in the age of groundwater. This study offers a scientific foundation for pinpointing areas with freshwater potential and elucidating the origins of saline groundwater in extremely arid regions.