This　study　focuses　on　the　nitrogen　(N)　and　phosphorus　(P)　removal　characteristics　in　a　simultaneous　nitrification　endogenous　denitrification　and　phosphorus　removal　(SNEDPR)　system　operating　at　different　sludge　retention　time　(SRT).　Four　extended　anaerobic/low　aerobic　(dissolved　oxygen:　0.5-1.0　mg•L-1)-operated　sequencing　batch　reactors　(SBRs)　fed　with　municipal　sewage　were　studied　at　different　SRT　of　5,　10,　15,　and　25　d.　The　experimental　results　show　that　a　shorter　SRT　at　an　SRT　≥10　d　enhances　the　competitive　advantage　of　PAOs　in　the　system　and　an　efficient　phosphorus　removal　performance　of　the　SNEDPR　system　was　achieved　at　a　SRT　of　10　d　and　15　d.　Especially　at　an　SRT　of　10　d;　the　average　PPAOs,　Anwas　68.4%,　the　PRA　and　PUA　reached　31.9　and　34.3　mg•L-1,　respectively.　The　nitrification　performance　of　the　system　was　not　affected　by　SRT　changes.　The　most　efficient　nitrogen　removal　performance　was　achieved　at　a　SRT　of　15　d,　with　a　high　average　TN　removal　and　SNED　efficiencies　reaching　89.6%　and　71.8%,　respectively.　At　a　SRT　≥10　d,　the　COD　removal　performance　of　the　SNEDPR　system　was　also　not　affected　by　SRT　changes.　The　COD　removal　efficiencies　were　higher　than　78%.　However,　when　the　SRT　was　shortened　to　5　d,　the　C,　N,　and　P　performances　of　the　system　worsened　due　to　the　loss　of　biomass;　the　SNED　and　PO43--P　removal　efficiencies　were　as　low　as　5.7%　and　0.5%,　respectively.　In　addition,　at　an　SRT=15　d,　the　sludge-settling　performance　of　the　system　was　the　best.　The　SV　and　SVI　were　20%　and　64　mL•g-1,　respectively,　and　the　sludge　concentration　increased　with　the　extension　of　the　SRT.　Under　long　SRT　(25　d)　operation,　the　system　showed　a　good　resistance　to　shock　loads,　but　the　sedimentation　performance　of　the　sludge　deteriorated.　©　2019,　Science　Press.　All　right　reserved.