Abstract: During the operation of coal mine underground reservoir, the roof caving rocks have a purification effect on mine water, but the mechanism of water-rock interaction is still unclear. In order to reveal the water-rock interaction mechanism in the underground reservoir of Daliuta Coal Mine, reservoir roof rock sample and mine water were studied. XRD, XRF, SEM and FT-IR were used to analyze the chemical composition and structure of roof rock samples. The static interaction experiments between five typical minerals in rock samples and mine water were carried out. Based on the conductivity of mine water and the concentration changes of K+, Na+, Mg2+, Ca2+ ions. The possible mechanism of water-rock interaction was discussed, and the adsorption isotherm behavior of Ca2+ on chlorite and its influencing factors were studied. The results show that the water-rock interaction in the reservoir includes the dissolution of soluble minerals in the roof rock samples, and the hydrolysis of albite, K-feldspar, kaolinite, illite and chlorite. The increase of K+ in the mine water is mainly from the hydrolysis of K-feldspar and illite. The roof rock sample has an adsorption effect on metal ions in the mine water. The adsorption effect of Mg2+ by the roof rock samples is greater than the Mg2+ released by the hydrolysis of chlorite in the roof rock samples. The decrease of Ca2+ is mainly caused by the adsorption of chlorite in the roof rock samples, and the precipitation of CaCO3 in mine water can also reduce the concentration of Ca2+. In addition, the water-rock interaction may include cation exchange of K-Mg and Ca-Mg. The adsorption process of Ca2+ by chlorite forms a non-uniform adsorption layer of multi-molecular layer, and the adsorption sites on the surface of chlorite are irregular, and the adsorption sites are not independent of each other.