Abstract: With natural mineral montmorillonite powder as gas explosion inhibitor, the effect of the concentration of montmorillonite powder on the characteristic parameters of explosion pressure and the average velocity of flame propagation at 9.5% methane-air premixed gas were tested using the 20 L spherical explosion device and the 5 L pipeline experimental system. The results showed that montmorillonite powder displayed a good suppression effect on methane explosion, the max-pressure of methane explosion and the average velocity of flame propagation of 9.5% methane-air premixed gas decreased firstly and then increased with the increased concentration of montmorillonite powder. The max-pressure of methane explosion, decreasing by 29.2%, was the lowest when the mass concentration of montmorillonite powder was 0.16 g/L in the 20 L spherical explosive device; in the pipeline explosion suppression test system, when the mass concentration of montmorillonite powder was 0.20 g/L, the flame propagation velocity was the lowest. In addition, the mechanism of the inhibition methane explosion by montmorillonite powder was also discussed.