In this study, DeNO_x process in a tubular reactor with corona discharge was investigated numerically using elementary reactions for NO-N_2 system. N, N_2, NO, NO_2, N_2O, O, O_2, NO_3 and O_3 were considered in this calculation. Formation rate of N radical by corona discharge was assumed to be proportional to electric current and N_2 concentration. The effects of initial NO concentration and gas flow rate on the DeNO_x performance were investigated. From the calculated results, it seems that the decrease of NO was caused by the reduction reactions of NO such as NO+N→N_2+O, rather than the oxidation reactions of NO such as NO+O→NO_2 or the reduction reaction of NO_2 such as NO_2+O→NO+O_2. Moreover, it was shown that the calculation model developed in this study can described the characteristics of DeNO_x process obtained by the experiment using the tubular reactor.