Sludge　retention　time　is　an　important　parameter　to　the　biological　phosphorus　removal　system.　This　paper　investigated　the　effect　of　long　sludge　retention　time　on　biological　phosphorus　removal　in　Anaerobic/Anoxic/Aerobic　process　(A2/O).　The　results　showed　that　prolonging　sludge　retention　time　(SRT)　of　the　A(2)/O　system　had　no　significant　impact　on　biological　phosphorus　removal　efficiency,　which　slightly　decreased　from　92.9%　(at　an　SRT　of　12　d)　to　92.1%　(at　an　SRT　of　30　d).　Scanning　Electron　Microscope-Energy　Dispersive　Spectrometer　(SEM-EDS)　analysis　demonstrated　the　relative　content　of　phosphorus　in　dry　activated　sludge　increased　from　2.27%　to　4.36%,　which　explained　the　excellent　phosphorus　removal　performance　at　long　SRT.　At　the　same　time,　the　average　particle　size　increased　from　201.57　mu　m　to　256.99　mu　m,　and　the　flocs　at　longer　SRT　had　a　more　spherical　and　compact　structure　relative　to　that　at　shorter　SRT.　Our　results　demonstrated　that　long　SRT　was　a　sustainable　way　for　biological　phosphorus　removal　in　A2/O　process.