To investigate the micromechanism of a multiple flammable gas explosion, CH4, CO, C2H6, C2H4, and H-2 were selected to determine the thermodynamic and dynamic characteristics of the gas mixture explosion using Gaussian software. The initiation mechanism and primary initiation pathway of the joint explosion of the five combustible gases were analyzed. A spherical experimental device for gas/dust explosions combined with a system for spectral measurements was implemented to obtain emission spectra of the.H radical and CH2O during the gas mixture explosion process. The oxidation reaction of CH4 initiated the chain reaction for the entire explosive reaction rather than the CO/C2H6/C2H4/H-2 mixture at the ignition moment of the explosion. Nevertheless, addition of the CO/C2H6/C2H4/H-2 mixture had obvious effects on the chain-branching reactions of the CH4 explosion. The (CH3)-C-center dot radicals produced during methane oxidation induced a hydrogen reaction, and H-center dot radicals generated in the reaction of (CH3)-C-center dot and H-2 triggered the involvement of other combustible gases in the explosion reaction, which considerably decreased the activation energy demand by multiple combustible gases to participate in the explosion reaction. The sequence of flammable gases involved in the explosion reaction was CH4, H-2, CO, C2H4, and C2H6. Furthermore, the experimental results indicated that the H-center dot radical appeared before CH2O during the explosion reaction process, which was consistent with the numerical simulation results. Moreover, the numerical simulation results provided a theoretical basis for the prevention of gas explosions and process safety in the petrochemical and mine industries.