Production rate of important reactants was calculated through grimech 3.0 mechanism in methane oxidation. A sensitivity analysis was employed to determine important elementary reactions in oxidation. A reduced kinetics mechanism for lean methane oxidation was built, including 16 species and 31 steps. Simulation results based on the reduced mechanism were compared with the calculation results of grimech 3.0. The reduced mechanism is suitable for lean fuel condition at an equivalence ratio lower than 0.2.