To　achieve　high　efficiency　of　nitrogen　and　phosphorus　removal　and　to　investigate　the　rule　of　simultaneous　nitrification　and　denitrification　phosphorus　removal　(SNDPR),　a　whole　course　of　SNDPR　damage　and　recovery　was　studied　in　a　pilot-scale,　anaerobicanoxic　oxidation　ditch　(OD),　where　the　volumes　of　anaerobic　zone,　anoxic　zone,　and　ditches　zone　of　the　OD　system　were　7,　21,　and　280　L,　respectively.　The　reactor　was　fed　with　municipal　wastewater　with　a　flow　rate　of　336　L/d.　The　concept　of　simultaneous　nitrification　and　denitrification　(SND)　rate　(r(SND))　was　put　forward　to　quantify　SND.　The　results　indicate　that:　(1)　high　nitrogen　and　phosphorus　removal　efficiencies　were　achieved　during　the　stable　SND　phase,　total　nitrogen　(TN)　and　total　phosphate　(TP)　removal　rates　were　80%　and　85%,　respectively;　(2)　when　the　system　was　aerated　excessively,　the　stability　of　SND　was　damaged,　and　r(SND)　dropped　from　80%　to　20%　or　less;　(3)　the　natural　logarithm　of　the　ratio　of　NOx　to　NH4+　in　the　effluent　had　a　linear　correlation　to　oxidation-reduction　potential　(ORP);　(4)　when　NO3-　was　less　than　6　mg/L,　high　phosphorus　removal　efficiency　could　be　achieved;　(5)　denitrifying　phosphorus　removal　(DNPR)　could　take　place　in　the　anaerobic-anoxic　OD　system.　The　major　innovation　was　that　the　SND　rate　was　devised　and　quantified.