Microplastics, a new type of contamination, were extensively distributed in water areas with increasing plastic production and poor management of plastic waste. Simultaneously, removing pollutants from water was a popular research topic in the field of water treatment. In this investigation of water treatment, simulated natural water containing polyethylene was treated using magnesium hydroxide and anionic polyacrylamide as dual coagulants. Based on a series of experiments, the optimum reactor conditions were an Mg²⁺ concentration of 40 mg/L, a pH of 12, and a temperature of 20℃. The maximum removal efficiency of polyethylene could reach 84.9% ± 3% under the optimal experimental conditions with the average size of flocs 57.19 μm. Using an intelligent Photometric Dispersion Analyzer, the full processes of coagulation-flocculation were recorded. Evaluating coagulationflocculation performance using flocs’ flocculation index and polyethylene removal efficiency as metrics. Scanning electron microscopy, Fourier transform infrared spectroscopy, and zeta potential were used to study the performance and coagulation characteristics. The results of this work confirm that the removal of microplastics relied on adsorption bridge and sweep flocculation mechanisms. This study provides a valuable theoretical basis for an in-depth comprehension of the performance and coagulation characteristics of removing polyethylene from wastewater.