Achieving　stable　partial　nitrification　(PN)　are　the　basic　guarantee　of　anaerobic　ammonia　oxidation　(anammox)　process.　However,　there　is　no　recognized　feasible　method　for　rapidly　achieving　stable　PN　in　municipal　wastewater,　and　further　research　is　necessary.　In　this　study,　paracetamol　was　proved　as　an　effective　nitrite　oxidation　inhibitor　through　long-term　experiment　lasting　392　days　in　three　systems　(floc　sludge,　granular　sludge,　biofilm).　PN　of　low-strength　ammonium　wastewater　was　rapidly　achieved　within　28　days　and　maintained　for　about　80　days　after　paracetamol　dose,　whereas　PN　recovered　again　within　10　days　and　sustained　over　150　days　under　paracetamol　dose　combined　with　low　dissolved　oxygen　strategy.　The　inhibition　effect　of　paracetamol　on　NOB　was　almost　not　affected　by　biomass　growth　modes.　QPCR　and　high-throughput　sequencing　showed　that　Nitrospira　(Oligotype　1)　was　inhibited　by　paracetamol,　and　PICURSt2　analysis　indicated　its　key　enzyme　NXR　was　significantly　downregulated　after　paracetamol　treatment,　which　were　the　key　reasons　of　PN　start-up　in　three　systems.　The　emergence　and　adaptation　of　Nitrotoga　was　the　main　reason　for　the　instability　of　PN.　This　study　proved　that　paracetamol　could　be　used　as　a　novel　nitrite　oxidation　inhibitor,　and　provided　a　possibility　to　achieve　the　mainstream　PN　and　anammox　for　treating　wastewater　with　low-strength　ammonium.