The new intensified combustion technology by using non-thermal equilibrium plasma in aero propulsion field causes more and more attention. Aimed at the study of the effect of plasma assisted combustion, the combustion characteristics of methane/air with active particle (O and H) and active group (OH) in non-thermal equilibrium plasma in firebox is investigated by numerical analysis. The result shows that plasma assisted combustion can greatly enhance flaming temperature by providing more free radicals and accelerating chain reaction, meliorate the temperature distributions and velocity distributions of the surface of outlet. By this plasma assisted combustion technique, the combustion efficiency can be increased and the discharge of pollutant decreased.