Anammox　granular　sludge　processes　are　an　attractive　and　efficient　biotechnology　in　the　field　of　wastewater　treatment.　In　this　study,　the　stratification　patterns　of　anammox　granular　sludge　bed　(GSB)　at　steady　states　were　illustrated　and　its　relationship　to　microbial　activity　and　community　were　systematically　investigated　under　different　nitrogen　loading　rates　(NLRs).　Morphological　observation　and　quantitive　particle　size　distribution　analysis　demonstrated　that　the　GSB　at　low　NLR　was　mainly　composed　of　micro　and　fine　granules　with　a　big　difference　between　bottom　and　top　sludge　layers.　But　at　high　NLR,　the　volumetric　mean　diameter　(VMD)　of　GSB　increased　with　the　size　distribution　width　(Span)　declined　forming　a　more　homogeneous　and　coarse　granules　population.　The　particle　size　distribution　parameters　of　GSB　could　be　fast　characterized　by　the　optical　lightness　(L*)　parameter　(r　=　−0.771,　p　＜　0.01,　n　=　16)　and　held　a　significant　correlation　with　the　nitrogen　removal　rate　(NRR)　of　anammox　system　(r　＞　0.9,　p　＜　0.05).　The　microbial　spatial　distribution　patterns　of　different　sludge　layers　were　further　investigated　by　high-throughput　sequencing.　The　microbial　community　α-diversity　index　and　microbial　abundance　matrix　proved　that　the　community　structure　tend　to　coverage　at　high　NLR.　Significant　difference　of　the　relative　abundance　of　microbial　community　was　detected　under　different　NLRs.　The　VMD　of　GSB　held　a　significant　correlation　with　the　relative　abundance　of　AnAOB　(r　=　0.556,　p　＜　0.01,　n　=　16)　and　other　common　accompanying　bacteria　(Denitratisoma　and　Chloroflexi).　This　study　proved　that　the　apparent　particle　size　distribution　patterns　of　GSB　could　be　a　potential　auxiliary　indicator　to　reflect　the　microbial　activity　and　community,　which　can　facilitate　the　innovative　process　monitor　of　anammox　system　based　on　visual　features.　©　2022　Elsevier　Inc.