Experiments of vented explosion were conducted in a 1 m3 vessel under the conditions of top ignition for premixed methane-air gas with a concentration from 7% to 13% to investigate the influence law of methane concentration on flame evolution and internal overpressure during the vented explosion process.The explosion venting mechanism was analyzed by analyzing the pressure-time curve and the flame evolution image.The results prove that concentration has a significant impact on the explosion venting characteristics of the methane-air premixed gas.The overpressure inside the container presents a double-peak phenomenon with a specific methane concentration.The first pressure peak P1 can appear at each concentration,while the second pressure peak P2 only occurs when the concentration is 9 %.P1 increases first and then decreases with the increase of concentration,while the trend of the timing of the peak is the opposite.However,both reach the extreme value at the methane concentration of 10%.This is mainly formed by the combined effects of initial flame propagation,external explosion,Helmholtz oscillation and Taylor instability,etc.The phenomenon that P2 is much higher than P1 is mainly formed by the mutual promotion of flame and sound pressure and the thermoacoustic coupling effect triggered by disturbance.The flame downward propagation velocity increases first and then decreases with the concentration,and reaches the maximum value when the methane concentration is 10%,and the combustion velocity is generally faster in the slightly rich combustion state.