Abstract: There is a large amount of rock in the underground reservoir. During the process of storage in the underground reservoir, there are water-rock interactions such as ion exchange, adsorption and leaching between mine water and rock in the underground reservoir, which affect the quality of mine water. The rock in the Halagou was collected, its cation exchange capacity(CEC) was measured, and the static adsorption-dissolution experiments under different chemical conditions(250 mg/L for Na⁺,Mg²⁺,K⁺,Ca²⁺) were carried out. The experimental results show that the CEC of rock is inversely proportional to the particle size. When the particle size is less than 120 mesh, the CEC reaches 134 mmol⁺/kg. The order of exchangeable base ions in rock is Exchangeable Calcium ≫ Exchangeable Magnesium > Exchangeable Sodium > exchangeable Potassium. After 48 hours of experiment, the ion concentration in each system tended to balance. The cation concentration in the Na⁺ system solution all increased, but in the other three systems, the original ions all decreased, and the K⁺ decreased the most. The order of the ion concentration exchanged from the caving roof rock to the aqueous solution from high to low is: Ca²⁺>Na⁺>Mg²⁺>K⁺,and the Ca²⁺ concentration still had an upward trend after the end of the test. After the reaction, the CEC of the rock increased to a certain extent, and the maximum CEC value under the Ca²⁺ system was up to 183.7 mmol⁺/kg. Based on XRD and other characterization results, it is further revealed that the leaching of non-clay minerals such as microcline, albite and pyrite can increase the concentration of Ca²⁺ and Na⁺ in the solution, while clay minerals such as illite and kaolinite adsorb/exchange cations in the solution through coordination. For cations, if leaching > ion exchange(the initial concentration is low),the concentration increases. On the contrary, it decreased. Therefore, when the content of Ca²⁺ and Mg²⁺ in mine water is high, the hardness of mine water can be reduced to a certain extent through water-rock interaction. This study provides a theoretical basis for the self-purification mechanism of mine underground reservoir.