To compare the effect of two different operational modes on partial nitrification (PN), two-stage continuous stirred-tank reactors (CSTR) 1# (anoxic-oxic) and 2# (controlling DO and HRT) were constructed and operated at room temperature (18-22℃). Start-up time, stability, aeration consumption, sludge settling ability, as well as the adaptability to the decreasing of ammonia nitrogen concentration were investigated. PN in 1# and 2# were accomplished in 26 d and 41 d, respectively. When the effluent of an anaerobic/oxic (A/O) process for phosphorous removing (containing ammonia nitrogen 35-43 mg/L) was used as influent, PN was stable both under 1# and 2# condition, however, aeration consumption could be reduced by about 20% in 2#. When the ammonia nitrogen decreasing from 43 to 27 mg/L, PN in 1# would be unstable and the rates of PN decreased to 67.39%. For comparison, PN in 2# could be maintained stable with an ammonia removal rate of >88%. Settleability of sludge was good both in 1# and 2#. Rapid start-up could be achieved through controlling DO and HRT, and a stable and efficient PN could be maintained through anoxic-oxic.