The combustion process of ventilation air methane (VAM) with air in a tangential coal-fired boiler was investigated by the component transport model. The influence of VAM with different volume fractions of methane (CH4) on the combustion characteristics of the boiler was analyzed. The results indicated that the maximum average temperature in the main combustion area increases to 102 K, with the increasing volume fraction of CH4 in the VAM. Under the same conditions, the distribution of oxygen (O2) volume fraction showed a trend of decay in the main combustion zone, while carbon monoxide (CO) started to increase. Meanwhile, the NO emission at the overfire air decreased from 974.8 mg/m3 to 436.3 mg/m3, with a reduction rate of 55.24%. When the VAM with the CH4 volume fraction of 0.75% was fed into the boiler for combustion in different ways, the furnace temperature would rise and the NO emission would decrease. The concentration of CH4 in the VAM should not be less than 0.01%. The analysis results demonstrated that adding the VAM into the boiler combustion cannot only save resources and protect the environment but also help to reduce the emission of nitrogen oxides.