The　process,　that　is　destruction　and　recovery　of　nitrification　performance　in　aqueduct　by　pre-chlorination,　is　simulated　by　a　BAR(bio-film　annular　reactor)with　addition　of　chlorine　in　different　ways.　The　results　showed　that　pre-chlorination　can　cause　larger　damage　to　the　bio-film　AOB　on　pipe,　and　give　significant　influence　on　removal　of　NH4+-N　and　NO2--N.　Higher　CT　value　is,　higher　growth　rate　AOB　during　recovery　stage　of　bio-film.　The　recovery　was　quicker　for　removal　performance　of　NH4+-N　(8　d)than　for　that　of　NO2--N(10　d).　Finally,　it　is　found　that　there　has　remarkable　correlation　between　amount　of　AOB　and　removal　rate　of　NH4+-N　in　pipe,　and　their　correlation　coefficient　can　reach　as　high　as　92%.　©　All　Rights　Reserved.