Abstract: Background With the rapid development of industry, the discharge of wastewater is increasing year by year, and the fluorine content in water is also rising, and the use of natural materials and industrial waste to remove fluoride has become a hot topic. Coal gangue is one of the largest industrial wastes in China, because it contains more clay minerals, the pore structure can be effectively improved through modification, so as to significantly improve its adsorption performance to achieve the effect of efficient removal of fluoride in water. Method This paper takes coal gangue and 200mg/L high-concentration fluorine-containing wastewater in the typical mining area of Henan Energy and Chemical Group Co., Ltd. as the research object, determines the modification conditions of coal gangue through single factor experiments, and combines scanning electron microscopy and organic element analysis to characterize and analyze. The adsorption mechanism of fluoride by modified gangue was comprehensively studied. Results and Conclusions The results showed that the original gangue and MgCl₂ were homogeneously mixed according to the mass ratio of 1:0.25, and the coal gangue fluoride removal material was prepared by roasting at 450 °C for 1.5 h, and the oscillation adsorption experiment was carried out under the conditions of feeding ratio of 20:1, temperature of 25 °C and rotation speed of 120 r/min, and the removal rate could reach up to 94.451%. Combined with the characterization analysis, it was found that the adsorption of modified gangue on F-mainly included electrostatic action, hydrogen bonding, ion exchange and precipitation complexation, and brucite peaks appeared inside the modified gangue, while mica substances and part of kaolinite were converted into amorphous silicon-aluminum compounds, and part of kaolinite was converted into illite, which enhanced the electrostatic adsorption and ion exchange in the gangue, and the beryllium fluoride in the gangue after adsorption of F- indicated that the modified gangue had adsorption effect on fluoride. The overall morphology of gangue is more loose, the specific surface area increases, and the relative content of metal oxides also increases, which is conducive to the removal of F- in water by precipitation, complexation and hydrogen bonding. The research findings of this paper can provide an important theoretical basis for the preparation of water treatment agents from coal gangue to treat wastewater.