We will apply in the plasma treatment technology from the research which controls the exhaust gas treatment. The N-O of active species increased with rf-power and flow rate in plasma. The removal ratio of hydrogen cyanide gas was higher at 40 watt than above 80 watt. In the case of the treatment of hydrogen cyanide at the lower rf-power, it was showed that restrained from the formation of NOx and the hydrogen cyanide had the higher removal ratio in this process.