Abstract: To increase the TN (total inorganic nitrogen) removal efficiency,a CANON (completely autotrophic nitrogen-removal over nitrite) reactor,which started directly under aerobic conditions in the laboratory was used.The temperature was controlled at 35 ℃±1 ℃,aeration rate was 31.2 m³/(m³·h),dissolved oxygen was about 1.5-2.0 mg/L,hydraulic retention time was 3.7 h respectively.Tests of ammonium and nitrite concentration on performance of CANON reactor were conducted.It is found that when the aeration rate is kept stable,it is not suitable to obtain high TN removal rate when the ammonium concentration is too high or too low.When the ammonium concentration is about 310-360 mg/L,a TN removal rate of more than 75% is gained under the above-mentioned conditions.Increasing the concentration of ammonium and nitrite in the reactor is beneficial to improve the TN removal load until both concentrations of ammonium and nitrite is more than 50 mg/L.When the CANON reactor is used to treat ammonium-rich wastewater without any organic carbon,the TN concentration in effluent is still high,and a further step is necessary to meet discharge standards.