The existing empirical formulae on gas explosion overpressure often ignore the influence of obstructions and barriers. Overpressures of series methane gas explosions occurred in a confined space were researched in logarithmic coordinates based on CFD method. The results indicated that the relation between the overpressure and the scaled distance is linear in logarithmic coordinates. Formulae on overpressure, combustion heat of the methane gas and distance from the centre of the combustible gas cloud were raised. This research can be used in calculations of explosion engineering, scientific research and others on methane gas explosion.