The mechanisms of the reaction of the diazocarbene radical (CNN) with the NO have been investigated by ab initio molecular orbital in conjunction with variational TST and RRKM calculations. The potential energy surface (PES) was calculated by the high-level CCSD(T)/aug-cc-PVQZ//B3LYP/6-311++G(3df,2p) method. From the calculated potential energy surface, we have predicted that the formation of N2O + CN (P5) is most favorable, and the calculated energies of reaction intermediates and transition structures along this path are all below the starting reference point. The predicted total rate constants, k(total), at a 760 Torr Ar pressure can be represented by the equations: k(total) = 2.47 x 10(-17)T(1.20) exp(1.60 kcal mol(-1)/RT) at T = 300-650 K and 2.49 x 10(-19)T(1.82) exp(2.29 kcal mol(-1)/RT) at T = 660-3000 K cm(3) molecule(-1) s(-1). The calculated results also indicate that the branching ratio for R-P5 in the temperature range 300-3000 K has the largest value. In addition, the rate constants for key individual product channels are provided in different temperature and pressure conditions. To rationalize the scenario of the calculated results, we also employ the Fukui functions and HSAB theory to seek for the possible explanation.