In order to study the interference effect of rarefaction wave on the laminar flame propagating structure and pressure characteristics of methane-air mixture, a small scale combustion chamber has been built. The techniques of high speed Schlieren photograph, pressure measurement and so on, are used to study the influence of rarefaction wave on the laminar flame propagating through methane-air mixture. The results show that, after the rarefaction wave acts on the propagation laminar flame, the laminar combustion is fully transformed into turbulent combustion just during several milliseconds, which leads to a sharp increase in the burning surface area and the pressure rise rate.