Flame propagation and combustion characteristics of methane/air mixed gas in gas explosion were studied in a constant volume combustion bomb. Stretched flame propagation velocity, unstretched laminar flame propagation velocity, unstretched laminar combustion velocity and Markstein length were obtained at various ratios of nitrogen to gas mixture. Combustion stability at various ratios of nitrogen to gas mixture was analyzed by analyzing the pictures of flame propagation. Furthermore, the effect of initial pressure on the flame propagation and combustion characteristics of methane/air mixed gas in gas explosion was analyzed. The results show that the unstretched laminar flame propagation velocity, the unstretched laminar combustion velocity, Markstein length, flame stability, and the maximum combustion pressure decrease distinctly with the increase of nitrogen fraction in the gas mixture. At the same ratios of nitrogen to gas mixture, Markstein length, unstretched laminar flame propagation velocity and unstretched laminar combustion velocity decrease and the maximum combustion pressure increase with the increase of initial pressure of the gas mixture. When nitrogen fraction in the gas mixture is over 20%, the flame will be unstable and is easy to exterminate. (C) 2012 Elsevier Ltd. All rights reserved.