The partial nitrification (PN) process was investigated at 30℃ in an air-lift circulation (ALC) reactor fed with simulated wastewater. The results proved that it was a highly-efficient process for ammonia removal. The turnover of the ALC reactor was 12—28 times per day with hydraulic retention time between 0.86 h and 2.00 h. When influent concentrations of ammonia were increased from 358.5 to 942.3 mg·L-1，the average volumetric ammonia removal rate reached as high as 5.5 kg N·m-3·d-1，which was at the top level reported in the literature. During the operation，the relative standard deviation of effluent substrate concentration，ammonia removal efficiency and nitrite accumulation was 4.3%—26.5%，3.1%—16.8% and 0.4%—5.3%，respectively，in spite of fluctuation of influent concentration，flow rate or pH. The stability of process performance could be attributed to both the efficient retention of sludge (4.0—5.2 g VSS·L-1) and the high specific activity of biomass (2.71 g N·（gVSS）-1·d-1 determined from the kinetic study).