The　collapse　of　mainstream　anammox　system　caused　by　deterioration　of　partial　nitrification　(PN)　is　easy　to　occur　and　it　is　vital　to　quickly　restore　the　stable　nitrogen　elimination　performance.　Herein,　a　novel　continuous　push-flow　anaerobic-oxic-anoxic–oxic　(AOAO)　process　treating　sewage　was　used　to　restore　the　nitrogen　elimination　performance　rapidly　under　deteriorated　PN.　The　increased　abundances　of　Nitrospira　and　Candidatus　Nitrotoga　was　responsible　for　the　deterioration　of　PN.　Effluent　total　inorganic　nitrogen　of　8.7　mg　N/L　and　a　stable　nitrogen　removal　rate　of　0.083　kg　N/m3·d　were　obtained　with　the　aerobic　hydraulic　retention　time　(HRT)　of　3.75　h　even　PN　deteriorated.　Endogenous　partial　denitrification　coupled　anammox　in　the　anoxic　zone　was　essential　to　maintain　stable　nitrogen　removal　under　the　deterioration　of　PN　and　the　anammox　contribution　increased　from　17.2　%　to　23.6　%.　The　AOAO　system　shows　robustness　on　nitrogen　removal　even　PN　deteriorated　under　the　decrease　of　HRT　from　16　to　12　h.　©　2022　Elsevier　Ltd