Abstract: Frequent explosion accidents caused by methane gas leakage pose significant safety concerns. Explosion venting is widely used as an explosion suppression measure in industrial fields. However,external secondary explosions can easily occur during the venting process,which increases the hazard severity. To address this,a numerical simulation study using FLUENT was conducted to establish a methane-air mixture explosion venting model in a square container. The effects of key parameters, including methane concentration,vent burst pressure,and vent diameter,on external flame evolution characteristics and pressure propagation behavior were systematically investigated. The results show that at a methane concentration of 9. 5%,a vent burst pressure of 20 kPa,and a vent diameter of 0. 5 m,the external flame propagation speed is higher,the flame front displacement increases,and the external secondary explosion response is most pronounced. Further analysis of the external secondary explosion pressure propagation characteristics reveals that when the methane concentration deviates from the near-stoichiometric value of 9. 5%,with the same vent burst pressure (20 kPa) and vent diameter (0. 5 m),the initial peak external pressure is higher,the fluctuation amplitude is larger,and the pressure duration is longer. These findings indicate that a reasonable match between vent burst pressure and vent diameter can effectively suppress external flame propagation and mitigate the secondary explosion pressure effects,providing a reference for optimizing methane explosion venting conditions and risk control.