Basing　on　qPCR　assay　and　15N　isotope　tracing　technique,　the　abundance,　rate,　role,　and　microbial　interaction　of　anammox　was　investigated　in　three　WWTPs　of　anaerobic-anoxic-oxic　(AAO)　process.　Results　showed　anammox　bacteria　was　detected　in　all　samples　with　abundance　of　106~107copies/g　VSS,　and　rate　of　0.11~0.90　μmol　N/(g　VSS·h).　As　for　the　microbial　interaction　among　anammox　and　other　microbial　process,　heterotrophic　denitrification　was　not　only　a　more　important　provider　but　a　stronger　competitor　for　NO2-,　compared　with　autotrophic　nitrification,　in　which　AOB　was　the　major　NO2-　producer.　The　roles　of　anammox　to　ammonia　oxidation　and　nitrogen　removal　were　calculated　to　be　2.55%~7.89%　and　2.07%~6.59%,　respectively,　and　the　role　of　anammox　in　summer　was　higher　than　that　in　winter.　Further,　canonical　correspondence　analysis　(CCA)　proved　the　temperature　is　one　of　the　key　environmental　variables,　and　nitri-　&　denitri-rates　were　primary　microbial　factors　for　anammox.　Results　suggested　although　the　abundance　of　anammox　bacteria　was　not　high,　the　widespread　of　anammox　played　an　overlooked　role　of　N　removal,　which　supplemented　N　balance　calculation　in　biological　wastewater　treatment　process,　and　provided　theoretical　support　for　the　realization　of　anammox　in　the　field　of　low-NH4+-N　sewage　treatment.　©　2016,　Editorial　Board　of　China　Environmental　Science.　All　right　reserved.