A reaction model for the conversion of methane to CI-oxygenates (methanol and formaldehyde) with NO, (x = 1, 2) has been proposed theoretically using the ab initio molecular orbital method. The geometric and electronic structures for all the present molecules have been calculated by means of the MP2 (frozen core)/ 6-311++G(2d,p) level of theory. On the basis of the optimized structures, the single paint calculations of the energies are carried out at the CCSD(T) level with the same basis sets. Through the theoretical analysis of the simplified CH4-NOx system instead of the experimental CH4-O-2-NO system, we found the possible reaction path leading to CI-oxygenates within all the barriers of less than 40 kcal/mol via CH3O at 800 K. NO2 has a higher activity for the hydrogen abstraction from methane than NO and O-2, though the calculated rate constants at 800 K indicate that this reaction is the rate-determining step in the conversion of methane to C-1-oxygenates. It is also found that increasing the concentration of NO promotes the yield of formaldehyde with the decreasing formation of methanol, which is consistent with recent experimental results in the CH4-O-2-NO system.