In　order　to　clarify　the　characteristics　of　anaerobic　ammonia　oxidizing　(ANAMMOX)　sludge　and　the　succession　rule　of　bacteria　based　on　particle　size　differentiation,　the　performance　change　and　microbial　community　structure　of　ANAMMOX　floc　sludge　during　the　formation　of　particles　in　the　reaction　system　of　a　high　ammonia-nitrogen　biofilter　were　studied.　The　results　indicated　that　the　specific　activity　(SAA)　and　tolerance　of　the　ANAMMOX　granular　sludge　(AnGS)　were　significantly　improved　by　increasing　the　particle　size,　and　the　SAA　of　R4(＞4.75　mm)　was　up　to　426.8　mg·(g·d)-1,　but　it　also　had　adverse　effects　on　mass　transfer.　The　results　of　the　high-throughput　sequencing　showed　that　dynamic　changes　between　bacterial　genera　were　common.　When　the　particle　size　was　less　than　4.75　mm,　the　increase　in　particle　size　strengthened　the　stability　of　the　bacterial　flora,　the　ammonia　oxidizing　bacteria　(AOB)　with　more　flocs　were　eliminated,　and　the　nitrogen　removal　ratio　gradually　stabilized.　R3　(2.8-4.75　mm)　exhibited　the　most　specific　flora　composition,　and　the　functional　bacteria　Candidatus　Kuenenia　accounted　for　52.7%,　while　the　R4　community　complexity　increased.　Furthermore,　the　proportion　of　functional　bacteria　decreased,　and　the　abundance　of　heterotrophic　bacteria　increased,　which　negatively　affected　the　particle　structure.　In　addition,　the　R3　microorganism　has　the　best　gene　function　expression　level,　which　is　significantly　better　than　small　particles　in　gene　replication　repair　and　energy　conversion.　Finally,　the　evolution　of　AnGS　was　analyzed　through　the　OTU　matrix　between　the　samples.　These　results　have　some　guiding　significance　for　the　optimization　of　the　AnGS　system　and　will　be　helpful　for　the　application　of　the　ANAMMOX　process.