Abstract: Based on the three-phase reaction experiments, taking CO₂ as the main gas phase, the typical minerals in coal as solid phase and mine water rich in iron and sulfate as liquid phase, the water-rock-gas reaction simulation experiment of closed gassy mine is carried out. The changes of chemical composition of mine water and coal mineral composition are compared and analyzed. The results have showed that in the mine water-rock-gas reaction, the pH value of the mine water increases and the Eh decreases, and the dissolution of mineral phase resulted in the increase of the content of Ca²⁺, HCO^3-, SO₄^2- and soluble SiO₂ in mine water, while the content of Mg²⁺ did not change significantly, the total Fe concentration decreased, and the salinity increased significantly. Typical minerals of coal and rock have different degrees of dissolution reactions. When calcite dissolves, new carbonate minerals will be generated in the reaction process, while pyrite dissolves with the generation of chlorite.