Abstract: The stability of performance of anaerobic ammonium oxidation (ANAMMOX) reactors was studied and the indices of performance stability were compared.The results showed that under different types of shock load, the reactors with different configurations displayed different stability.The biofilm reactor stood first in stability towards substrate shock load, followed by anaerobic sequencing batch reactor (SBR) and the granular sludge bed.And the biofilm reactor took the first place towards hydraulic shock load, followed by the granular sludge bed and SBR.The three ANAMMOX reactors were more tolerant to hydraulic shock load than to substrate shock load.When different kinds of stability assessment indices(i.e., sensitivity ratio, mean variance ratio and derivative regression function) were used, inconsistent assessment conclusions were reached.It was suggested that the mean deviation ratio and derivative regression function were more effective and universal.