It is realized short-cut nitrification and denitrification in an A/O pilot-scale plant treating actual domestic wastewater controlling DO concentration (0.5 mg/L) in low level at normal temperature, the average nitrite accumulation rate reached 85 % or above. Three operational modes: low DO short-cut nitrification and denitrification (Mode 1), low DO complete nitrification and denitrification (Mode 2) and high DO complete nitrification and denitrification (Mode 3) were briefly compared, based on the nitrogen removal, operating cost, sludge characteristics and operational mechanism. Experimental results showed that the Model is the best modes of biological nitrogen removal, in terms of improving nitrogen removal and reducing operating cost. The net pH change in aerobic zones and anoxic zones is high for Mode 1, but the net pH change in anoxic zones is very small for Mode 3. The nitrification rate is the smallest for Mode 2, and the nitrification rate for Mode 3 is little higher than that of Mode 1; the denitrification rate for Model is larger than that of Mode 3 about 15 %. It is feasible using DO and pH on-line sensors to control the nitrification process.