For　the　stable　operation　of　simultaneous　nitrification-endogenous　denitrification　and　phosphorus　removal　(SNEDPR)　system　under　domestic　sewage,　sequencing　batch　reactor　(SBR)　was　selected　to　inoculate　SNEDPR　granular　sludge　under　artificial　water　distribution.　The　actual　domestic　sewage　and　sludge　were　pretreated　by　mixed　hydrolysis　acidification　and　taken　as　the　influent　matrix,　and　the　stable　operation　of　the　system　was　realized　by　optimizing　the　pretreatment　unit　hydraulic　retention　time　(HRT)　combined　with　SBR　sludge　discharge　modes.　Results　showed　that　when　the　HRT　of　the　pretreatment　unit　decreased　from　12　h　to　4　h,　the　content　of　acetic　acid,　propionic　acid,　and　the　proportion　of　volatile　fatty　acids　(VFA)　provided　by　the　hydrolytic　acidification　solution　increased,　the　anaerobic　poly-hydroxyalkanoate　(PHA)　storage　in　aerobic　granular　sludge　(AGS)　increased,　the　simultaneous　nitrification　and　denitrification　(SND)　efficiency　increased　to　58.　1%,　and　the　effluent　TN　decreased　to　about　7.　8　mg　/　L.　At　the　same　time,　under　bottom　sludge　discharge,　the　proportion　of　small　particles　in　SBR　increased,　LB-EPS　increased,　and　the　settlement　performance　of　the　system　became　worse.　The　proportion　of　mature　and　aged　large　particles　under　top　sludge　discharge　increased,　and　the　moisture　content　and　strength　of　particles　decreased.　Under　selective　sludge　discharge,　the　particle　size　in　SBR　was　concentrated　in　0.　5　-　0.　9　mm,　with　dense　particle　structure　and　high　strength.　The　layered　distribution　of　bacteria　in　the　particles　enhanced　the　SND　effect.　Batch　experiments　showed　that　the　activities　of　nitrite-oxidizing　bacteria　(NOB)　and　glycogen　accumulating　organisms　(GAOs)　were　reduced,　the　proportion　of　denitrifying　polyphosphate　accumulating　organisms　(DPAOs)　with　NO2-　as　electron　receptor　in　the　system　was　increased　to　40.　5%,　and　the　efficiency　of　simultaneous　nitrification　and　endogenous　denitrification　phosphorus　removal　was　improved.　The　short　HRT　combined　with　selective　sludge　discharge　of　the　pretreatment　unit　had　stable　performance　in　the　treatment　of　domestic　sewage　particles.　The　effluent　TN　and　TP　met　the　first-level　A　standard　specified　in　GB　18918—2002　Discharge　Standard　of　Pollutants　for　Municipal　Wastewater　Treatment　Plant.　The　system　can　achieve　efficient　and　stable　removal　of　nitrogen　and　phosphorus.　©　2023　Harbin　Institute　of　Technology.　All　rights　reserved.