Partial　denitrification　granular　sludge　(PDGS)　and　denitrification　granular　sludge　(DGS)　play　an　important　role　in　nitrogen　removal　from　wastewater.　However,　the　inherent　cause　of　aggregation　capacity　related　to　the　ratio　of　COD　to　nitrogen　(COD/N)　is　still　unclear.　In　this　study,　metabolomics　analysis　was　combined　with　microbiological　analyses,　granular　performance　and　extracellular　polymeric　substances　(EPS)　structure　to　explore　the　granulation　mechanism　at　different　influent　COD/N　ratios.　The　results　showed　that　the　higher　COD/N　ratio　selectively　enhanced　the　gluconeogenesis　pathway,　purine　and　pyrimidine　metabolism　pathway,　resulting　in　more　extracellular　polysaccharide　(PS)　excretion　and　floc　sludge.　The　absence　of　carbon　source　weakened　tricarboxylic　acid　cycle　(TCA)　reaction,　resulting　in　NAD+　and　ADP　decrease,　nitrite　accumulation　and　change　of　microbial　community　structure.　The　amino　acids　biosynthesis　pathway　was　enhanced　under　low　COD/N　ratio,　which　promoted　the　hydrophobicity　of　EPS.　PDGS　had　stronger　Acyl-homoserine　lactones　(AHLs)-based　quorum　sensing　(QS)　than　DGS　during　the　operational　period.　CO8-HSL,　C8-HSL　and　C6-HSL,　as　the　main　form　of　AHLs,　played　a　dominating　role　in　DGS　and　PDGS.　Batch　tests　illustrated　that　adding　AHLs　obviously　improved　the　synthesis　of　the　amino　acids,　threonine　(Thr),　tryptophan　(Trp),　methionine　(Met)　and　glycine　(Gly).　Dosing　AHLs　regulated　PS　synthesis　only　at　a　high　COD/N　ratio.　The　glucose-6P,　glycerate-3p　and　UDP-Glc　were　upregulated　only　in　DSG,　which　increased　the　hydrophilic　groups　in　EPS.　The　results　not　only　provided　the　new　insights　into　the　metabolism　of　denitrifying　granular　sludge,　but　also　indicated　the　application　potential　of　the　technologies　regarding　start-up　and　operation　of　granule　sludge.