The heterotrophic nitrification aerobic denitrification (HNAD) process can withstand the environment with high NH 4 + -N concentration and complex components, and has the potential to be an effective scheme for nitrogen removal of anaerobically treated leachate from municipal solid waste incineration plant. But its mechanism is still unclear and the NH 3 stripping process has received little attention. At the same time, the high concentration of NH 4 + -N in the anaerobically treated leachate also has great recycling potential. In this study, typical HNAD microorganisms were enriched and used for nitrogen removal from anaerobically treated leachate. A one-step system with a total nitrogen removal ratio of more than 98 % was constructed. Isotopic labeling experiments showed that nitrogen was not the main product. The important role of NH 3 stripping in the HNAD system was defined, and 46.63 % nitrogen was recovered on this basis.