Coal gangue is one of the biggest industrial solid waste in China, and it is widely used in the field of wastewater treatment as adsorbent. However, there are a lot of crystal water and clay mineral impurities in the natural coal gangue. If natural coal gangue is directly used to treat wastewater, there are some problems such as low efficiency, long time and large dosage. In this experiment, ZnCl₂ was used to modify coal gangue to reduce the crystal water and clay mineral impurities, increase the specific surface area of coal gangue, improve the treatment efficiency and reduce the treatment cost. Through the modification experiments under different conditions, the modified coal gangue needed for this experiment is obtained. At the same time, the structure and chemical composition of the modified coal gangue are changed compared with the original coal gangue. ZnO has replaced SiO₂ as the main chemical composition of zinc modified coal gangue, the Zn²⁺ loading on the surface of coal gangue increases the specific surface area of coal gangue, changes the internal structure of coal gangue, and improves the ability of treating phosphorus-containing wastewater with coal gangue as adsorbent. Through the adsorption treatment of 50 mg/L simulated wastewater containing phosphorus by zinc-modified coal gangue, the optimum adsorption conditions were obtained as follows:The dosage of zinc-modified coal gangue was 1 g/L, the pH was 5 and the temperature was 30℃. In addition, Ca²⁺ and Mg²⁺ can promote the adsorption of phosphate on zinc-modified coal gangue.