A new microwave catalytic reactor system was developed. By coupling the catalytic effect of microwave irradiation with the reducing activity of activated carbon, the microwave catalytic reduction of nitric oxide (NO) was studied in activated carbon bed. Novel results were observed under microwave irradiation. The conversion of NO to N2 under microwave irradiation remarkably increased compared to conventional heating, which indicates that the microwave irradiation has microwave catalysis effect besides thermal effect. The exhaust gas temperature under microwave irradiation was much lower compared to that of conventional heating; there are different adsorption mechanisms of activated carbon under different heating modes. The effects of a series of reaction parameters, including reaction temperature, microwave power, NO concentration, O2 concentration and gas hourly space velocity(GHSV) on the productivity of N2 with a new microwave catalytic reactor system were investigated. The results show that NO is converted predominantly to N2 under all reaction conditions and the highest conversion of NO to N2 is up to 99.8% under optimized conditions.