To reduce the emission of the strong greenhouse gas nitrous oxide (N₂O) in partial nitritation system, a lab-scale SBR treating synthetic high-ammonium wastewater (around 600 mg·L-1 of influent ammonia) was investigated for the effect of pH values (7.5,8.0 and 8.5) on N₂O emission. The results showed that, the N₂O emission was observed under different pH values, and the total amount of N₂O emission decreased with pH value increment. At pH 7.5,8.0 and 8.5, the N₂O emission amount accounted for 3.81％, 2.35％ and 2.00％ of the influent ammonium nitrogen, respectively. At pH 7.5, in the initial 50 min the N₂O emission rate firstly increased (maximum value of 44.5 μg·min-1·g-1) and then returned around 26.4 μg·min-1·g-1. At pH 8.0 and 8.5,3.7 and 22.9 μg·min-1·g-1 of maximum N₂O emission rate were achieved in the initial 50 min, respectively, however, they increased slowly with the pH decrease and nitrite accumulation.