Abstract: To systematically evaluate the effects of CO on CH4 -Air explosion and their regime,the flammable limits of CH4 with CO addition were measured using a standard test device. The explosion parameters and the flame emission radiation intensity (I)-time curves of three intermediate products ( H∗,OH∗,and CH2 O∗ ) in the explosion process were measured synchronously in a closed spherical combustion tank equipped with flame spectra detecting system. By exploring the relationship between the intermediate products and the explosion pressure through a comparative analy- sis,the effects of CO on CH4 -Air explosion were analyzed in a micro-to-macro level. Results show that CO increases the risk of CH4 explosion,reduces the critical oxygen volume fraction,and significantly increases the amount of N2 re- quired to completely render CH4 inert. The effect of CO on the CH4 explosion pressure mainly depends on the amount of oxygen and its chemical properties. In the oxygen-rich condition,CO will aggravate the explosive intensity of the premixed system. This effect will be gradually weakened with the oxygen reduction in the system,and the damping effect will be exhibited under the condition of oxygen-lean. The effect of CO on the maximum pressure (Pmax ) of CH4 and on the maximum radiation intensity (Imax ) of intermediate products is consistent. The change rules regarding the time of Pmax and Imax align with each other. The time at which the intermediate product starts to accumulate is correlated with the explosion intensity of the main combustible gas in the premixed system. Furthermore,a massive,rapid accu- mulation of intermediate products is one of the causes of the aggravating of the system explosion. The presented data will be helpful to improve the understanding of the intrinsic mechanism of gaseous explosion hazards,providing a theo- retical basis for developing and improving potential chemical suppressant. Attention can be paid to develop and im- prove the chemical suppressants that damp the key free radicals directly. By improving its capacity of breaking chain- reactions,the corresponding suppression effect would be enhanced.