Vacuum chamber is a new method to suppress the gas explosion. The explosion propagation characteristics have been studied in an L-shaped channel (tubes joined a right angle) with a vacuum chamber in the region of joining of the tubes. The vacuum chamber separated from the inner tubular space with the help of a diaphragm pierced by firing pin. The results demonstrate that the effect of explosion suppression of vacuum chamber is related to the break-up time of diaphragm and the position of the explosive flame front. When the diaphragm breaks up, the shorter the distance of flame front propagation is, the closer the flame front gets to the vacuum chamber, and the better effect of explosion suppression is, conversely, the worse the effect of explosion suppression is.