Coal gangue (CG) has dense structure and excellent internal crystallization. After modification, its pore structure can be enlarged and become an adsorptive material with good adsorption performance, which is a good idea to recover solid waste of CG to a certain extent. At the same time, the content of organic matter in the wastewater of medical intermediate is high. Modified CG can be used as an ideal material for the adsorption treatment of medical intermediate wastewater. Herein, the CG was treated with three activation methods of high-temperature calcination, freezing microwave and acidification treatment to investigate their adsorption behavior to p-hydroxybenzenesulfonic acid. SEM, FTIR, XRD, XPS and BET were used to study the microstructure of raw and modified CG. The relationship between the activation methods and the structure of the CGs was established. The specific surface area of calcined CG increases obviously, which is attributed to the elimination of interlayer water. Acidification treatment can effectively activate the chemical structure of CG surface. By using ultraviolet spectrophotometer, both the kinetics and thermodynamics of the adsorption processes are investigated and fitted with the kinetic equations and adsorption thermodynamic equations. Results indicate that the CG treated with acidification method has the best adsorption effect on p-hydroxybenzenesulfonic acid, and the maximum removal rate reaches 85.34%. The quasi-second-order rate equation and Freundlich model are adopted to analyze the adsorption kinetics and thermodynamics, and results show that the adsorption process includes both physical adsorption and chemisorption. Overall, the relationships of activation method-microstructure-adsorption performance are revealed, which is significant to guide the application of CG in the adsorption field.