Considering　the　shortage　of　organic　materials　for　biological　nitrogen　removal　from　wastewater　under　low　C/N　ratios,　two　methods　are　proposed　in　order　to　achieve　high　efficiency　of　biological　nitrogen　removal;,　making　full　use　of　the　carbon　source　and　reducing　the　requirement　of　carbon　source.　To　make　full　use　of　carbon　sources,　modified　biological　nitrogen　removal　process　are　introduced,　including　the　anoxic/oxic　step　feeding　process　and　the　pulsed　SBR　process.　To　reduce　the　carbon　source　requirement　in　biological　nitrogen　removal,　novel　biological　nitrogen　removal　processes　are　introduced,　including　short-cut　nitrification　and　denitrification,　the　anaerobic　ammonium　oxidation　(ANAMMOX)　process　and　completely　autotrophic　nitrogen　removal　over　nitrite　(CANON)　process.　The　mechanisms,　the　advantages,　the　unsolved　problems　and　the　applications　of　these　technologies　and　processes　are　analyzed.