Expanded　Granular　Sludge　Bed　(EGSB)　reactor　was　used　as　the　start-up　device　of　the　CANON　process　in　this　experiment,　in　the　effects　of　different　upflow　velocity　on　the　nitrogen　removal　performance　of　the　Completely　Autotrophic　Nitrogen　removal　Over　Nitrite　(CANON)　process　was　investigated.　The　change　of　particle　size　of　granular　sludge　in　Integrated　Fixed-film　and　Activated　Sludge　(IFAS)　system　and　the　biomass　of　biofilm　were　quantitatively　analyzed.　In　addition,　high-throughput　sequencing　analysis　was　carried　out　for　microorganisms　on　granular　sludge　and　biofilm　to　explore　the　characteristics　of　microbial　community　structure　on　different　aggregates.　The　results　showed　that　the　total　nitrogen　removal　rate　(NRR)　increased　from　0.20kg/(m3•d)　to　0.66kg/(m3•d)　in　the　continuous　operation　process　when　the　upflow　velocity　increased　from　2m/h　to　6m/h.　The　ratio　of　ΔNO3--N/ΔNH4+-N　was　steadily　kept　at　0.11,　a　realization　of　the　efficient　and　stable　operation　of　CANON.　When　the　upflow　velocity　increased　to　8m/h,　the　nitrogen　removal　performance　of　CANON　process　was　unstable,　the　NRR　decreased　to　0.42kg/(m3•d),　and　the　average　particle　size　of　sludge　decreased　from　1.3mm　to　0.9mm.　When　the　upflow　velocity　restored　back　to　6m/h,　the　nitrogen　removal　performance　of　CANON　process　gradually　recovered.　Ultimately,　the　NRR　was　stabilized　at　0.60kg/(m3•d),　the　average　particle　size　of　sludge　was　restored　to　1.2mm,　and　the　specific　growth　rate　of　biofilm　biomass　was　0.0024d-1.　High　throughput　sequencing　showed　that　Aerobic　Ammonia　Oxidation　Bacteria　(AerAOB)　functional　bacteria　Nitrosomonas　(2.45%)　and　Anaerobic　Ammonia　Oxidation　Bacteria　(AnAOB)　functional　bacteria　Candidatus　kuenenia　(2.38%)　were　the　main　genera　in　the　granular　sludge.　The　main　bacteria　in　the　biofilm　were　AnAOB　functional　bacteria　Candidatus　kuenenia　(9.78%)　and　Candidatus　brocadia　(4.23%),　while　a　small　amount　of　AerAOB　functional　bacteria　Nitrosomonas　(0.40%)　were　also　detected.　The　results　suggested　that　there　were　some　differences　in　two　microorganisms　in　different　aggregates.　©　2021,　Editorial　Board　of　China　Environmental　Science.　All　right　reserved.