Abstract: Research of dissolved organic matter (DOM) adsorption by coal gangue was carried out. Coal gangue was from coal mine underground reservoir and was characterized by SEM, BET, BJH, and XRF. The effects of the coal gangue dosage, temperature, and initial DOM concentration on DOM removal by coal gangue were investigated. Results show that the coal gangue has a lamellar structure with well-developed inter-particle pores. The BET specific surface area of the coal gangue was 5.697 m²/g. A 0.748 mg/g equilibrium adsorption capacity and 74.78% DOM removal efficiency were gotten under the conditions of 20 mg/L DOM concentration, 20 g/L coal gangue, 25 ℃, and 12 hours adsorption time. The DOM adsorption by coal gangue can be well described by Langmuir isotherm and quasi-second-order kinetic model. The adsorption process was monolayer adsorption and was mainly chemical adsorption. The thermodynamic analysis shows that the adsorption process is a spontaneous endothermic reaction. DOM removal performance and mechanism by coal gangue in high-salinity mine water system were deeply explored. The research results may provide a theoretical support and technical guidance for safe storage of water in underground reservoir with high-salinity mines (represented by the Ningdong mining area), and give an insight for solving the problem of water shortage in the western coal mining areas.