This study presents a novel way of using a red mud (RM)-based composite powder to suppress polyethylene (PE) dust explosions. Porous modified red mud (MRM) was prepared via acid-alkali treatment and served as the carrier. Co3O4 and NaHCO3 were loaded via ball-milling dry coating and solution impregnation, yielding a new composite powder suppressant denoted as MRM-Co3O4-NaHCO3. The explosion suppression performance of the composite powder against low-density polyethylene (LDPE) dust explosions was experimentally evaluated in a 20L spherical explosion vessel and a transparent pipe flame propagation apparatus. The results indicate that the new suppressant substantially reduces explosion pressure and suppresses flame propagation(with a 30% addition level, the maximum explosion pressure was reduced by 56.9% and the flame velocity decreased by 61%). Among the five samples tested, suppression efficiency follows the order: MRM-Co3O4-NaHCO3 > MRM-Co3O4> NaHCO3 > MRM > Co3O4. Microstructural characterization reveals a multi-mechanism synergy: MRM as a porous carrier provides physical encapsulation and isolation; NaHCO3 endothermically decomposes into CO2 and H2O, contributing to physical cooling and gas-phase inerting; Co3O4 catalytically oxidizes highly reactive small-molecule hydrocarbons into CO2 and H2O, lowering combustible gas content. Overall, through the combination of physical barrier, thermochemical heat absorption, and catalytic oxidation, MRM-Co3O4-NaHCO3 represents an efficient pathway for suppressing PE dust explosions, providing a new potential for resource utilization of industrial solid wastes.