Abstract: In order to find a gas explosion suppression medium which can not only protect the environment but also suppress gas explosion and solve the explosion problem in gas transportation, analysis was carried out in this paper on the explosion suuppression mechanism of heptafluoropropane as an explosion suppression medium, and with a 20 L explosion test vissel, study was made on the influence of the heptafluoropropane in different volume concentration upon the maximum explosion pressure, the maximum explosion pressure rise rate and peak pressure of the premixed methane-air containing 9.5% of methane. It was found out in research that under the experimental condition, when the ignition delay time was 60 ms, the lowest heptafluoropropane concentration for suppressing the premixed methane-air explosion was 17.4%; when the heptafluoropropane concentration was 5% to 17%, both the maximum explosion pressure and maximum rate of pressure rised with the increase of the heptafluoropropane concentration, and the heptafluoropropane had a promotion for the premixed methane-air explosion. This research showed that the heptafluoropropane could be used as a new environmentally friendly medium for suppressing the gas explosion, but the reseasoable dosage of the heptafluoropropane should be determined in its using process according to the condition of its using place.