Experimental investigations were conducted on the process of combustion and explosion vent in a 200 mm (diameter) x 400 mm (length) vertical cylindrical vessel. When CH(4)-air mixture gases were used and the vent diameter was 55 mm, conditions of Phi (equivalent ratio)=0.8, Phi=1.0 and Phi=1.3 and two ignition positions (at the cylinder center and bottom) were selected. The venting processes and the correlated factors are discussed in this paper.