Abstract: A gas blast experiment system is established in this paper. The regularity and characteristics of gas blast loading is investigated by 19 tests with respect to gas concentration, vent glass failure strength and vent area. The analysis results show that when the gas concentration of methane is 7.5%~10.5%, there are two pressure peaks produced by indoor methane gas explosion, the combustion is acoustically unstable, and the second peak is larger than the first one. When the gas concentration of methane is larger than 10.5%, there is no acoustic phenomenon with only one pressure peak, and the peak is mainly affected by the cover of the vent window. When the gas concentration of methane reaches 9.5%, the internal gas blast pressure is the maximum because of vigorous reaction. Increasing vent glass failure pressure gives rise to the first pressure peak, and increasing vent area results in the slight drop of the first pressure and the drastically decrease of the second peak. The results may be helpful for knowing the regularity and characteristics of internal gas blast loading and investigating the response and failure patterns of structure under gas blast loading.