Abstract: To effectively prevent and control potential methane explosion hazards during coal mining, mesoporous Al₂O₃ was synthesized via the cetyltrimethylammonium bromide (CTAB) template method using bauxite as the raw material. Silane coupling agent KH550 was grafted onto the surface of mesoporous Al₂O₃ by the impregnation method, and a KH550-Al₂O₃ composite explosion suppressant was successfully prepared. The microstructures of the samples were characterized by Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and laser particle size analysis. On the basis of a 20 L spherical explosion vessel test platform, the explosion suppression performance of the KH550-Al₂O₃ composite suppressant with different mass concentrations on premixed methane/air mixtures was investigated, and its explosion suppression mechanism was revealed with the aid of density functional theory (DFT). The experimental results show that KH550 is grafted onto the Al₂O₃ surface through Si–O–Al bonds without damaging its mesoporous structure and crystalline properties, and the dispersibility of modified powder is significantly improved. The optimal mass concentration of the composite suppressant for explosion suppression is 0.32 g/L. At this concentration, the maximum explosion pressure is reduced to 0.56 MPa with a reduction rate of 35.6%, the pressure rise rate drops to 2.55 MPa/s with a reduction rate of 68.6%, and the flame wave temperature decreases to 548 K with a reduction rate of 50.0%. The explosion suppression mechanism relies on the synergistic effect of physical and chemical actions. Physically, mesoporous Al₂O₃ inhibits flame propagation and controls temperature via heat dissipation and physical barrier effects; the pyrolysis products of KH550 dilute the volume fractions of methane and oxygen and form a thermal insulation layer. Chemically, KH550 decomposes at high temperature to release NH₃, which captures ·H and ·OH radicals directly or indirectly through four reaction pathways with low energy barriers and consumes oxygen simultaneously, thus terminating the chain reaction and achieving efficient explosion suppression.