In order to explore more utilization approaches of coal gangue and achieve the goal of “treating waste with waste”，in this study，coal gangue was taken as raw material to successfully synthesize the high-molecular composite coagulant，polyaluminium magnesium zinc chloride（PAMZC），through a series of steps，including high-temperature calcination，hydrochloric acid leaching，doping with magnesium and zinc elements，polymerization，and aging.The effects of n（Zn）/n（Al），n（Mg）/n（Al），polymerization pH value and polymerization time on the coagulation performance of PAMZC were explored.FT-IR，XRD，SEM and point-scan spectroscopy were used to characterize the structure and morphology of PAMZC.The results showed that when n（Zn）/n（Al） was 0.25，n（Mg）/n（Al） was 0.15，polymerization pH value was 2.25 and the polymerization time was 4 h，PAMZC had the best coagulation performance.The turbidity of the effluent after coagulation was decreased to 0.97 NTU，and the removal rates of turbidity and total phosphorus reached 99.18% and 88.85%，respectively.FT-IR and XRD indicated that a polymerization reaction occurred among zinc，magnesium and aluminum elements，resulting in the formation of high-molecular polymers with a relatively high degree of polymerization.The SEM results showed that the surface of the structural units of PAMZC was uneven，with intricate pores formed，increasing the number of adsorption vacancies，which was beneficial for enhancing the coagulation performance.PAMZC performed well in the removal of turbidity and total phosphorus，and its effect was significantly better than that of the commercially available PAC.Therefore，PAMZC was also regarded as an efficient phosphorus removal agent.