Abstract: In order to study the influence of low air pressure conditions on the formation characteristics and pathway of CO and NO_x in methane premixed combustion, the detailed numerical simulation was carried out by using Chemkin software. According to the latest spectral data used by the Python language self-programmed program, the Planck average absorption coefficient was calculated and imported into Chemkin software to improve the calculation accuracy of radiation heat transfer. Results show that the combustion temperature of methane, concentration distributions of NO and OH at low air pressure can be accurately predicted by using Konnov 0.6 mechanism and the Planck average absorption coefficient calculation method in the radiation model. In addition, with the decrease of air pressure, the temperature in the front of the premixed combustion furnace decreases while that in the back increases gradually. The decrease of air pressure leads to the increase of CO formation rate and decrease of CO consumption rate, resulting in the increase of CO production and decrease of burn-out rate. The NO produced by the premixed combustion of methane and air was mainly from prompt-NO and NNH-NO, and the contribution of the prompt-NO and NNH-NO increases slightly with the decrease of air pressure.