The　morphological　structure,　properties,　microbial　community　and　function　of　anammox　biofilms　induced　by　large-pore　carriers　(Bls),　small-pore　carriers,　filament　carriers　and　non-carriers　(Bn)　in　low-strength　wastewater　were　comprehensively　studied.　The　carriers　promoted　biomass　accumulation　and　agglomeration,　with　Bls　demonstrating　the　highest　biomass　proportion　of　0.76,　the　highest　specific　anammox　activity　(0.41　kgN/(kgVSS·d)−1)　and　the　largest　aggregates.　Hydraulic　shearing　stimulated　Bn　to　secrete　most　extracellular　polymeric　substances　and　capture　more　inorganic　ions　for　enhanced　strength.　Metagenomic　sequencing　showed　that　the　four　biofilms　shared　a　common　core　flora,　but　differed　in　cross-metabolism.　The　proportion　of　the　functional　bacterium　Candidatus　Brocadia　was　highest　in　Bls,　while　the　increase　in　heterotrophic　bacteria　in　Bn　supported　stronger　metabolic　capacity.　Finally,　the　proposed　anisotropic　or　isotropic　carrier　structure　was　identified　as　the　key　to　generating　＇uniform　development＇　and　＇central　development＇　models.　This　study　is　helpful　for　understanding　the　anammox　aggregation　mechanism　and　carrier　optimization.　©　2022　Elsevier　Ltd