Abstract: In view of the fragility of the ecological environment in the west, water resources protection is particularly important in the west, and coal development will directly affect the water quality through mine water pollution, damage the groundwater system and other ways, so it is necessary to solve the coal-water contradiction. Taking the Ulan Mulun River Basin as a case study, given the significant impact of coal mining activities on water quality, an in-depth study of the water-coal interaction mechanism and the water quality development process is of great significance in balancing the relationship between rational coal resource development and water resource protection. Based on the long-term immersion test of the Ulan Mulun River water with non-stick coal and long-flame coal, we studied the evolution process of their hydrochemical characteristics and verified it by hydrogeochemical simulation. The water in the study area was characterized by weak alkalinity and low mineralization after immersion, and the water of the Ulan Mulun River after immersion with non-stick coal and long-flame coal samples showed some differences in hydrochemical components, with HCO₃·Cl-Na and HCO₃·SO₄-Na as the main hydrogeochemical phases after immersion, respectively. Whereas, the simulation paths showed that sulfate dissolution and cation exchange are important hydrogeochemical processes affecting water quality in the study area. Rock salt dissolution and silicate weathering were the main pathways of Na⁺ increase in the leaching solution, and HCO₃⁻ originated from CO₂ escape and dissolved into the water body causing carbonate mineral dissolution. Based on the in-depth study of the interaction between water resources and coal and the evolution mechanism of water quality in the Ulan Mulun River Basin, the key process of water-coal co-evolution is revealed, which provides a scientific basis and basic reference for the sustainable development of coal resources and the effective protection strategy of water resources in the Yellow River Basin.