The mechanism of non-thermal equilibrium plasma assisted combustion is recommended. In this paper the assisted combustion effect of methane is calculated by using the Gibbs free energy theory. Based on the analysis of the burning temperature and the combustion products after the injection of various quantity particles, the chemical kinetic characteristic of plasma can expedite the process of reaction, increase the burning temperature and reduce the ejection of the pollutant, which verifies that the use of plasma to assist combustion in aero engine combustion chamber is feasible.