Abstract: Based on the K- turbulence model and the eddy dissipation combustion model, the explosion venting to the air in a cylindrical vessel filled with the stoichiometric methane-air mixture was simulated using the colocated grid SIMPLE scheme. The dominant mechanisms of the occurrence of the secondary explosion during the venting processes were elucidated according to the numerical and relevant experimental results. After venting, there existed the low pressure area of rarefaction wave and the high pressure area of suspended shock inside the external combustible cloud forming from the discharged combustible gas. Under some suitable venting conditions, the violent combustion in the high pressure area was induced by the flame jet, which gave rise to the pressure increasing rapidly, and even the secondary explosion.