Significant　progress　in　understanding　the　key　enzymes　or　species　of　anammox　has　been　made;　however,　the　nitrogen　removal　mechanism　in　complex　coupling　systems　centered　on　anammox　remains　limited.　In　this　study,　by　the　combination　of　metagenomics-metatranscriptomics　analyses,　the　nitrogen　removal　in　the　anammox-centered　coupling　system　that　entails　partial　denitrification　(PD)　and　hydrolytic　acidification　(HA,　A-PDHA)　was　elucidated　to　be　the　nitrogen　transformation　driven　by　the　electron　generation-transport-consumption　process.　The　results　showed　that　a　total　nitrogen　(TN)　removal　efficiency　of　＞98%,　with　a　TN　effluence　of　＜1　mg/L　and　a　TN　removal　contribution　via　anammox　of　＞98%,　was　achieved　after　59　days　under　famine　operation　and　alkaline　conditions　during　the　start-up　process.　Further　investigation　confirmed　that　famine　operation　promoted　the　activity　of　genes　responsible　for　electron　generation　in　anammox,　and　increased　the　abundance　or　expression　of　genes　related　to　electron　consumption.　Alkaline　conditions　enhanced　the　electron　generation　for　PD　by　upregulating　the　activity　of　glyceraldehyde　3-phosphate　dehydrogenase　and　strengthened　electron　transfer　by　increasing　the　gene　encoding　quinone　pool.　Altogether,　these　variations　in　the　electron　flow　led　to　efficient　nitrogen　removal.　These　results　improve　our　understanding　of　the　nitrogen　removal　mechanism　and　application　of　the　anammox-centered　coupling　systems　in　treating　nitrogen　wastewater.