Abstract: Three emitted gaseous nitrogen compounds were traced, when high strength ammonia containing wastewater was treated in a sealed intermittent reactor by Simultaneous Nitrification and Denitrification （SND） process. The emitted NO₂ amount was less than background value of the laboratory. NO₂ was therefore neglected. However, emitted NO and N₂O were more than 10 times of the background. Less N₂O was emitted under low DO and high pH condition. Under different DO mass concentration conditions, it was obtained by diagrammatic integral method that about 0.58% and 6.53% of total lost nitrogen was emitted as NO and N₂O, respectively（DO mass concentration is 1.5～3.0 mg/L）, and 0.48% and 39.34% of total lost nitrogen was emitted as NO and N₂O, respectively （DO mass concentration is 2.5～4.0 mg/L）. Moreover, the available means to control N₂O emission was discussed.