Anaerobic　ammonia　oxidation　bacteria　(AnAOB)　are　difficult　to　cultivate　due　to　their　long　start-up　time　and　sensitivity　to　environmental　conditions.　In　this　study,　anammox　granular　sludge　was　cultured　with　ordinary　activated　sludge　under　influent　dissolved　oxygen　concentrations　of　6-8　mg/L,　successfully　enriching　AnAOB.　The　presence　of　multiple　microorganisms　in　the　activated　sludge　enabled　the　anammox　system　to　resist　the　unfavorable　influent　environment　and　sustain　system　stability.　The　total　nitrogen　removal　rate　reached　a　maximum　of　81%,　and　the　TN　effective　load　increased　from　0.1　to　1.5　kg　N/m(3)/d.　The　results　showed　that　the　dissolved　oxygen　present　in　the　influent　did　not　lead　to　a　breakdown　in　the　anammox　system.　The　protein　in　the　sludge　extracellular　polymeric　substances　played　an　important　role　in　the　enrichment　of　AnAOB,　and　the　sludge　settling　performance　at　the　bottom　of　the　reactor　was　better　than　that　at　the　top　of　the　reactor,　with　protein/polysaccharide　in　the　range　of　5-6.3.　Candidatus　brocadia　and　Candidatus　kuenenia　were　the　main　anammox　functional　bacteria　in　the　system.　On　153　d　of　reactor　operation,　their　relative　abundances　were　8.51　and　5.68%,　respectively.　This　study　shows　that　microorganisms　in　activated　sludge　contribute　to　the　stability　of　the　anammox　system　when　the　influent　conditions　are　appropriate.　This　provides　a　new　idea　for　the　rapid　start-up　of　the　anammox　system　and　enrichment　of　AnAOB.