The external explosions may occur in an explosion venting and give a potential risk. However, the basic dynamic process of external explosions during the venting to ambient air is yet not well understood. In this paper, a series of vented explosion tests in high failure pressure has been conducted in a cylindrical venting vessel. It has been demonstrated clearly from the pressure-time histories and the shadowgraphs of the external flow field that under some suitable venting conditions there exist two peak pressures in the external flow field, one is generated from the membrane rupture and the other is induced by the external explosion due to the violent combustion of the vented combustible gas. The effects on the flow patterns outside the venting vessel under different failure pressures, vent areas (blockage ratio) and chemical equivalent ratios are also discussed in the term of the experimental results. Moreover, the venting process was simulated numerically by using SIMPLE schemes in colocated grid, based on the k-? turbulent model and ‘eddy dissipation combustion model’. The calculated results are in good agreement with the measured results. The dominant mechanisms of the occurrence of the external explosion during the venting processes have been elucidated based on measured and calculated results.