The　formula　of　theoretical　nitrogen　removal　efficiency　for　the　step　feed　biological　nitrogen　removal　process　was　re-deduced　based　on　the　mass　balance　of　nitrate　nitrogen　and　verified　by　the　experiments.　Nitrogen　removal　efficiency　under　uniform　influent　flow　distribution　ratios　and　different　influent　flow　distribution　ratio　was　verified　under　different　C/N　ratios.　Under　the　condition　of　C/N　ratio　6,　8.25　and　10.5　(COD　concentration　was　maintained　at　330　mg/L)　with　uniform　influent　flow　distribution　ratio　in　each　stage,　the　nitrogen　removal　efficiency　was　80.1%,　79.8%　and　81.3%　respectively　corresponding　to　the　theoretical　value.　Under　the　condition　of　high　C/N　ratio　10.5,　13　and　17.5(NH3-N　concentration　was　maintained　at　38　mg/L)　with　different　influent　flow　distribution　ratios　in　each　stage,　nitrogen　removal　efficiency　were　studied.　The　experimental　results　showed　that　nitrogen　removal　efficiency　was　92.4%,　93.8%　and　96.4%　respectively　with　influent　flow　distribution　ratio　λ　of　2.5,　3　and　4　respectively,　higher　than　that　of　reported　articles　and　corresponding　to　the　value　of　this　paper.