The　current　researches　on　microorganisms　in　anammox　system　were　mainly　focused　on　anaerobic　ammonium　oxidation　bacteria.　The　microbial　community　structure　and　the　key　kinetic　parameters　of　anaerobic　ammonium　oxidation　bacteria　(AnAOB),　ammonia　oxidizing　bacteria　(AOB),　nitrite　oxidizing　bacteria　(NOB)　and　denitrifying　bacteria　(DNB)　in　anammox　filter　were　measured　and　analyzed　in　this　study.　Moreover,　the　effects　of　DO　concentration　in　the　range　of　0.2~1.5mg/L　on　the　activity　of　AnAOB,　AOB　and　NOB　were　investigated.　The　results　showed　that　the　anammox　filter　of　long-term　stable　operation　was　still　a　mixed　system　with　multiple　bacterial　groups,　in　which　anammox　bacteria　was　the　main　function　bacteria.　The　activity　of　AnAOB　with　5.3mgN/(gVSS•h)　was　the　highest　among　the　functional　bacteria　in　the　filter;　whereas　DNB　and　AOB　had　a　certain　activity.　When　DO　concentration　increased　from　0.2mg/L　to　1.5mg/L,　the　activity　of　AnAOB　almost　kept　stable;　whereas,　the　specific　ammonia　oxidation　rate　of　AOB　increased　from　0.76mgN/(gVSS•h)　to　1.08mgN/(gVSS•h).　The　obtained　oxygen　half　saturation　constant　(KO2,　AOB)　of　AOB　was　(0.106　±　0.010)　mg/L,　which　indica　ted　that　AOB　has　high　affinity　for　oxygen.　During　the　entire　experiment,　the　activity　of　NOB　was　not　detected.　Therefore,　in　the　anammox　system,　the　main　functional　bacteria　coexisted　and　competed　each　other　for　substrates.　©　2021,　Editorial　Board　of　China　Environmental　Science.　All　right　reserved.