Abstract: In order to prevent the shock load of high concentration of NH₄⁺-N on A/O system, the comparisons of single A/O process and step feed two-stage A/O process (the ratio of influent volume during the two feeds was 7:3) on the treatment of liquor wastewater with high NH₄⁺-N were conducted. The concentration of NH₄⁺-N, NO₂^--N, NO₃^--N and COD_Cr in the effluents was efficiently reduced by the step feed two-stage A/O process. The removal efficiencies were respectively enhanced by 16.9%, 43.2%, 49.7% and 8% comparing with that in single A/O process. The reasons could firstly attribute to the supplements of required carbon sources and NH₄⁺-N for the short-cut nitrification and denitrification in the secondary feed, which was beneficial to the removal of NO₂^--N and NO₃^--N. Meanwhile, the efficient utilization of carbon sources and the removal of NO₂^--N also contributed to the reduction of COD_Cr in the effluents. Moreover, the step feed two-stage A/O process could also relieve the inhibitory effects of NH₄⁺-N and NO₂^--N on the microbial activities of ammonia oxidizing bacteria and nitrite-oxidizing bacteria, which was superior to the further removal of NH₄⁺-N in aerobic process of the second A/O stage. However, the step feed two-stage A/O process had little effects on the removal of PO₄^3-. The accumulation of NO₂^--N in the secondary A/O stage made the reactor into anoxic state. It would result in the inadequate release of phosphorus and then reduce the potential of phosphorus uptake by phosphorus-accumulating bacteria in oxic condition. The results indicated that the step feed two-stage A/O process could remarkably enhance the removal efficiency of typical pollutants (NH₄⁺-N, NO₂^--N, NO₃^--N and COD_Cr) in liquor wastewater.