Abstract: At present, most of the research on gas explosion takes the mixed gas of CH₄ and air as the research object, but the gas explosion in coal mine is not a separate CH₄ explosion, there are often CO and other components, which have a certain effect on gas explosion. In order to reveal the effect mechanism of CO on gas explosion reaction, the explosion pressure of 9.5% CH₄ and 0-4% CO mixed gas is measured in a 20 L spherical explosion tank. The results show that with the increase of CO concentration, the maximum explosion pressure of the mixed gas increases first and then decreases, and the maximum explosion pressure is 624.9 kPa when the CO volume fraction is 2%. In the numerical simulation software of Chemkin-Pro, the temperature sensitivity and key free radicals of the gas explosion reaction of CO, CH₄ and air mixed gas are analyze from the chemical kinetics point of view by adopting the GRI-mech 3.0 mechanism, and the effect mechanism of CO on gas explosion reaction is obtained. Adding a small amount of CO to 9.5% CH₄ can make the fuel concentration in the explosion reaction system close to the actual stoichiometric value. At this time, the promotion effect of CO on the gas explosion reaction is dominant. Macroscopically, the maximum explosion pressure increases with the increase of CO concentration. As the concentration of CO continues to increase, the explosion reaction system appears lean oxygen state, the 98 and 120 elementary reactions that hinder the temperature increase are promoted, and the 57 and 170 elementary reactions that promote the temperature increase are inhibited. Macroscopically, it is reflected that with the increase of CO concentration, the temperature of the explosion reaction system decreases, and the maximum explosion pressure decreases. CO delays the appearance time of the peak amount of substance concentration of free radicals, and the ignition delay time of the explosion reaction increases after adding CO, thereby reducing the explosion reaction rate.