Compared with conventional free flame,porous medium combustion flame has higher power density,wider flammability limit,higher combustion rate and lower pollutant emission. In order to investigate the combustion flame and pollutant emission characteristics of methane porous medium,the combustion characteristics of premixed gas in three-dimensional alumina pellet porous medium burner were numerically simulated by using computational fluid dynamics (CFD) method and GRI-Mech 3.0 mechanism. The effects of equivalence ratio on flame surface,combustion reaction rate and emission characteristics of CO and NOx were analyzed. The results show that the CH4/air combustion goes through three stages:preheating-combustion-burnout,and reaches the peak of temperature and combustion reaction rate in the main combustion zone. In the second half of the main combustion zone and the burn out zone,the combustion temperature tends to be uniform,which is an important difference between porous medium combustion and traditional combustion. There is no linear relationship between the effect of chemical equivalence ratio on the overall combustion characteristics of methane/air porous media,when the stoichiometric ratio is 1.0,the overall combustion characteristics are better. The NO concentration in porous media combustion field first increases rapidly due to the influence of thermal NO generation mechanism,and then a certain concentration of NO is consumed by the reduction reaction involving NO in GRI-Mech 3.0 mechanism due to the enhancement of reducing atmosphere.