The　reinforcement　of　short-cut　denitrification　towards　simultaneous　nitrogen　and　phosphate　removal　was　investigated　in　a　step-feed　alternating　anoxic-oxic　sequencing　batch　reactor　(SAOSBR)　treating　real　domestic　wastewater　with　low　C/N　ratio.　Meanwhile,　the　mechanism　of　improving　biological　phosphorus　removal　by　short-cut　denitrification　was　also　analyzed.　Nitritation　was　achieved　with　the　nitrite　accumulation　rate　(NAR)　of　above　95%,　which　attribute　to　starving　treatment　and　alternate　with　anoxic　and　aerobic.　This　nitritation　enhanced　the　simultaneous　nitrogen　and　phosphate　removal,　and　the　average　removal　rate　of　total　nitrogen　and　phosphate　increased　by　about　6%　and　36%,　respectively.　Batch　experiments　also　indicated　that　the　carbon　source　competition　between　denitrifying　bacteria　with　phosphorus　accumulating　organisms　(PAOs)　was　weaken　while　nitrite　was　used　as　electron　acceptor　for　denitrification　under　the　condition　of　insufficient　carbon　source.　The　reason　of　enhanced　biological　phosphorus　removal　was　that　residual　nitrite　had　small　effect　on　anaerobic　phosphorus　release　in　PAOs.　Thereby　the　quantity　of　anaerobic　phosphorus　release　and　poly-β-hydroxyalkanoate　(PHA)　synthesis　in　PAOs　were　enhanced.　Therefore,　short-cut　denitrification　was　more　advantageous　in　removing　phosphorus　in　treating　wastewater　with　limited　carbon　source.　©,　2014,　Chinese　Society　for　Environmental　Sciences.　All　right　reserved.