Nitrous　oxide　(N2O)　is　an　inevitable　intermediate　generated　during　the　nitrogen　removal　process　of　granule-based　simultaneous　nitrification　and　denitrification　(SND)　system.　In　order　to　alleviate　N2O　production　while　maintaining　a　desired　total　nitrogen　(TN)　removal　level　in　this　system,　a　comprehensive　evaluation　of　the　contribution　pathways　and　process　parameters　affecting　N2O　turnovers　is　keenly　required.　Therefore,　mathematical　models　were　applied　to　evaluate　the　impact　of　operating　conditions　and　unravel　potential　mechanisms　on　TN　removal　performance　and　N2O　production.　Simulation　results　show　that　higher　N2O　production　(11.6　%–14.2　%)　occurs　at　higher　dissolved　oxygen　(DO)　concentrations,　lower　chemical　oxygen　demand　(COD)　levels,　longer　hydraulic　retention　time　(HRT)　and　larger　granule　size　in　the　granular　SND　system.　The　relative　conversion　rates　of　nitrogenous　components　in　different　regions　within　the　granule　influence　N2O　turnovers,　with　the　nitrification　process　occurring　only　in　the　region　200　μm　inward　from　the　granule　surface　and　denitrification　working　throughout　the　entire　granule.　In　the　inner　region　of　the　granule　(0–300　μm),　the　heterotrophic　bacteria　(HB)　denitrification　pathway　dominates　N2O　production　as　a　source　of　N2O.　While　in　the　outer　region　(300–450　μm),　HB　denitrification　acts　as　a　sink　for　N2O　and　regulates　N2O　turnovers　(i.e.　production　and　reduction　of　N2O)　together　with　the　hydroxylamine　(NH2OH)　pathway　that　is　the　main　contributor　of　N2O　production.　Moreover,　simultaneous　adjustment　of　multiple　operating　parameters　within　a　certain　range　can　lower　the　N2O　production　factor　(<0.5　%)　while　achieving　the　desired　TN　removal　efficiency　(>80　%),　resulting　in　a　feasible　N2O　mitigation　strategy.　©　2023　Elsevier　B.V.