In order to understand the mechanism of C-NO reaction, the detailed material balance was established by analyzing all the gas species produced during the reaction with mass spectroscopy and gas chromatography. The amount of nitrogen-containing surface species was estimated in the temperature range between 600 and 950 degrees C and with NO concentration of, mainly, 540 ppm. Then the effect of surface species on the reaction rate was examined. The step response experiments were carried out by switching the feed gas from (NO)-N-14-O-16 to (NO)-N-15-O-18. The results reveal not only the reaction mechanism but also the depletion rate of surface nitrogen species during the experiment. N-2 formation rate was correlated with NO concentration and the amount of surface nitrogen species. It is concluded that N-2 is mainly formed by the first-order reaction between C(N) and NO.