To　achieve　high　nitrification　and　denitrification　rates,　step-feed　SBR　with　multiple　aerobic　and　anoxic　phases　was　adopted　to　study　nitrogen　removal　performance.　Theoretical　analysis　of　step-feed　SBR　was　presented　first,　from　which　feeding　steps　and　C/N　ratio　had　significant　influences　on　nitrogen　removal　performance.　Total　nitrogen　removal　efficiency　would　increase　with　increasing　of　feeding　steps,　while　the　increasing　extent　was　not　distinct　with　feeding　steps　above　4.　At　a　given　feeding　step,　nitrogen　removal　efficiency　would　also　increase　with　increasing　of　C/N　ratio.　Experimental　work　was　conducted　in　a　lab-scale　SBR　to　investigate　practical　effects　of　these　critical　factors,　using　real　municipal　wastewater.　The　results　showed　when　C/N　ratio　was　appropriately　decreasing　influent　flow　mode　could　achieve　enhanced　nitrogen　removal　with　less　adding　of　external　carbon　source,　compared　with　equal　influent　flow　mode.　Three-step　equal　influent　flow　mode　was　recommended　to　treat　common　municipal　wastewater　in　view　of　operation　complexity.　Non　steady-state　experiments　over　about　three　months　confirmed　step-feed　SBR　was　an　enhanced　nitrogen　removal　process　with　high　efficiency.　Total　nitrogen　in　the　effluent　was　under　2　mg/L,　the　average　removal　efficiency　achieved　for　TN　was　over　97%　just　adding　a　little　external　carbon　source,　and　good　sludge　settleability　was　obtained.