Abstract: The high-salinity mine water generated during coal mining in the border area of Inner Mongolia and Shaanxi poses a significant challenge to regional water resource development and utilization as well as ecological environment protection. Therefore, it is crucial to investigate the hydrochemical characteristics and genetic mechanism of high-salinity mine water in this mining area. To this end, 166 sets of mine water samples were collected from 55 coal mines across Dongsheng Coalfield, Northern Shaanxi Jurassic Coalfield, and Junggar Coalfield. Systematic analysis of the hydrochemical data was conducted using methods including mathematical statistics, Durov diagrams, Gibbs diagrams, and ion ratio analysis, thereby clarifying the hydrochemical types, hydrogeochemical processes, and major ion sources of mine water in different coalfields of the study area. The results show that the hydrochemical characteristics of mine water in the Inner Mongolia-Shaanxi border area exhibit significant spatial variability: the mine water in the eastern and southern regions has relatively stable pH values and low total dissolved solids (TDS) mass concentrations; whereas in the arid western and northern regions, both the pH values and TDS mass concentrations of mine water are relatively high. Further analysis reveals that the spatial distribution of mass concentrations of Na⁺+K⁺, Ca²⁺, Mg²⁺, Cl⁻ and SO₄²⁻ in mine water of Northern Shaanxi Jurassic Coalfield varies greatly; the spatial distribution of HCO₃⁻ mass concentration in mine water of Dongsheng Coalfield also shows notable differences. Distinct differences exist in the hydrochemical types and major ion sources of mine water among different coalfields: the dominant hydrochemical type of mine water in Dongsheng Coalfield and Northern Shaanxi Jurassic Coalfield is HCO₃·Cl·SO₄-Na type, where Ca²⁺ and Mg²⁺ are mainly derived from the weathering and dissolution of silicate minerals; by contrast, the mine water in Junggar Coalfield is dominated by SO₄·Ca-Mg type, with Ca²⁺ and Mg²⁺ primarily originating from the dissolution of calcite, dolomite, and gypsum. The dominant anion in the mine water of the study area is SO₄²⁻, which is mainly generated from the dissolution of gypsum and the oxidation of pyrite in coal-bearing strata.