Partial　nitritation/anammox　(PN/A)　has　been　recognized　as　a　cost-efficient　process　for　wastewater　nitrogen　removal.　The　addition　of　carriers　could　help　achieve　biomass　retention　and　enhance　the　treatment　efficiency　by　forming　the　dense　biofilm.　However,　accurately　determining　the　abundance　of　anammox　bacteria　(AnAOB)　to　evaluate　the　biofilm　development　still　remains　challenging　in　practice　without　access　to　specialized　facilities　and　experimental　skills.　In　this　study,　we　explored　the　feasibility　of　utilizing　the　morphological　features　of　anammox　biofilm　as　an　indication　of　the　biofilm　development　progression,　and　its　correlation　with　microbial　communities　was　also　revealed.　The　time-series　biofilms　from　an　integrated　fixed-film　activated　sludge　(IFAS)　system　with　stable　PN/A　performance　were　sampled　representing　the　different　biofilm　development　stages.　The　biofilm　morphological　features　including　color　and　texture　were　respectively　quantified　by　red　(R)　coordinate　and　Local　binary　pattern　(LBP)　descriptor　via　image　processing.　Hierarchy　clustering　analysis　proved　that　the　extracted　morphological　descriptors　could　well　distinguish　the　different　stages　(colonization,　succession,　and　maturation)　of　biofilm　development.　The　microbial　community　dynamics　of　time-series　anammox　biofilms　were　investigated　using　the　amplicon　sequence　variant　(ASV)　analysis.　Candidatus　Brocadia,　as　the　typical　AnAOB,　dominated　in　the　whole　communities　of　16.3%–20.0%,　moreover,　the　biofilm　development　was　found　to　be　driven　by　distinct　Brocadia　species.　Linear　regression　evidenced　that　the　Brocadia　abundance　could　be　directly　correlated　to　the　value　of　R　and　LBP,　and　the　total　variation　of　microbial　communities　could　be　significantly　explained　by　the　morphological　features　via　redundancy　analysis.　This　study　demonstrates　a　new　way　to　monitor　the　biofilm　development　by　extracting　the　visible　features　of　anammox　aggregates,　which　can　help　facilitate　the　automated　control　of　anammox-based　bioprocess.　©　2023　Elsevier　Ltd