Effects　of　short　hydraulic　retention　time　(HRT)　in　wet　weather　and　long　HRT　in　dry　weather　on　sludge　properties,　microbial　community,　and　metabolomic　of　anammox　granular　system　were　studied.　Results　showed　under　equal　nitrogen　loading　rate　(0.4　kg　N/(m3　·　d))　conditions,　an　HRT　of　4.41　h　was　beneficial　for　total　nitrogen　removal　efficiency　(78.9　%).　The　shorter　the　HRT,　the　lower　the　particle　density　(1.01±0.34　g/cm3),　the　lower　the　settling　performance　(1.18±0.28　cm/s),　and　the　worse　the　biomass　retention　(1.04±0.18　g/L),　but　the　higher　the　mechanical　strength　(85.22　Pa).　Properly　decreasing　HRT　could　increase　the　permeability　of　anammox　granules,　ensuring　their　activity.　Metabolomics　analysis　indicated　that　the　activity　of　anaerobic　ammonium　oxidizing　bacteria　was　promoted　by　stimulating　the　metabolic　pathways　of　amino　acids　and　glycerophospholipids.　In　summary,　this　research　clarified　the　effect　of　wet/dry　weather　on　anammox　granular　system　and　provided　theoretical　guidance　for　the　application　in　engineering.　©　2024　Elsevier　Ltd