The possible energy pathways for the reactions of N2 with singlet and tripled C2O have been investigated at the CCSD(T)/6-311+G(3df)//B3LYP/6-311+G(3df) level of theory. Our results show that the rate-controlling transition states for the formation of 3CNN + CO, NCO + CN and 3NCN + CO through triplet surface have 36.2, 57.7 and 60.5 kcal/mol barriers relative to the reactants 3C2O + N2. Formation of 1CNN + CO and 1NCN + CO via the singlet surface needs to overcome 43.7 and 66.9 kcal/mol barriers. The dominant products are 1,3CNN + CO and cyc-1NCN + CO, their rate constants in cm3 molecule-1 s-1 can be presented as k1 (3CNN + CO) = 3.5 × 10-11 exp(-36.8 kcal/mol/RT), k2 (1CNN + CO) ≤ 2.9 × 10-12 exp(-33.2 kcal/mol/RT) and k3 (cyc-1NCN + CO) = 6.86 × 10-20exp(-27.7 kcal/mol/RT), which are significantly lower than those assumed in the literature. The rate constants for the formation of 3NCN + CO and NCO + CN are too small to be important due to their high exit barriers. The predicted heats of reaction for formation of products NCO + CN, 3CNN + CO and 3NCN + CO are 45.9, 18.1 and -10.7 kcal/mol, which agree excellently with the experimental values, 45.8, 17.7 and -10.7 kcal/mol. Our results imply that the reaction of C2O with N2 cannot compete with the CH + N2 reaction for prompt-NO formation in hydrocarbon combustion.