Abstract: Mg(OH)₂-coated Al(OH)₃ composite flame-retardant was prepared with a chemical compound technique. SEM, X-ray energy dispersion spectroscopy (X-EDS) and XRD were used to investigate the composite flame-retardant, and the results show that the particles of fine Al(OH)₃ powder are rough and coated with Mg(OH)₂ nanoparticles in the composite flame-retardant. The specific surface area of particles increase from 3. 797 9 m²·g^-1 to 15. 941 4 m²·g^-1 by coating. EVA products filled with the composite retardant have superior flame retardancy (the oxygen index is 39.0) and mechanical properties (the tensile strength is 10.2 MPa, the elongation at break is 180%) to those with uncoated Al(OH)₃ and the physical mixture of Al(OH)₃ and Mg(OH)₂. Thermal analysis (TG-DTA) demonstrates that the composite flame-retardant could increase the decomposition temperature and burning residue rate of the EVA products, bate the thermal cracking of polyethylene's main chain effectively, and promote the charring.