In this paper, a minimal skeletal mechanism involving 20 species and 56 reactions was generated for CH4/O2/CO2 mixtures from the GRI Mech 3.0 mechanism. The directed relation graph-aided sensitivity analysis (DRGASA) method was applied for mechanism reduction at the first step. Then, principle component analysis (PCA) was used for further reduction. The chemical reality of the generated skeletal mechanism was checked by the reaction pathways analysis of CH4/O2/CO2 mixtures in a constant-pressure ignition process. Finally, the generated skeletal mechanism was validated by the ignition delay times, laminar flame speeds, important species concentrations, and extinction turning points in the conditions of various pressures, temperatures, O2/CO2 ratios, and equivalence ratios. Results showed that the developed skeletal mechanism could reproduce the results from the detailed mechanism.