Nitrification-denitrification　biological　nitrogen　removal　process　has　become　the　hotspot　for　the　wastewater.　During　carbon/nitrogen　(C/N)　ratio　was　1.16,　2.25,　4.07　and　6.20,　the　change　of　denitrification　efficiency　and　the　impact　on　the　partial　nitrification/denitrification　was　investigated.　The　results　showed　that　removal　rate　of　ammonia　nitrogen　was　maintained　in　the　high　level,　and　was　stable　above　98%　after　C/N　ratio　higher　than　1.16.　With　C/N　ratio　increased,　the　removal　rate　of　chemical　oxygen　demand　was　increased　about　20%,　total　nitrogen　was　increased　from　54.9%　to　84.6%.　Simultaneously,　after　C/N　ratio　was　higher　than　4.07,　the　concentration　of　effluent　TN　was　below　15　mg/L.　Nitrite　accumulation　rate　was　maintained　above　95%,　the　effect　on　partial　nitrification　was　good,　and　the　concentration　of　effluent　nitrate　was　nearly　0,　the　best　ratio　of　the　C/N　ratio　was　4.07.　©　(2014)　Trans　Tech　Publications,　Switzerland.