Influence　of　pre-chlorination　on　pipeline　biofilm　water　purification　efficiency　and　recovery　process　were　studied　using　BAR　reactors　simulating　water　delivery　pipeline.　The　results　showed　that　the　amount　of　heterotrophic　bacteria　quickly　reduced　after　chlorination　and　almost　no　ammonia　oxidizing　bacteria　was　detected.　However,　short　impact　was　conducive　to　biofilm　update　and　bacterial　regrowth　potential　was　enhanced.　Having　resumed　operation　for　240　and　144　hours,　the　amount　of　heterotrophic　bacteria　and　ammonia　oxidizing　bacteria　of　pre-chlorination　biofilm　was　higher　than　control　group.　Ammonia　nitrogen　degradation　was　evidently　reduced　after　chlorination,　removal　efficiency　dropped　from　79.01%　to　32.1%,　14.46%　and　9.88%　respectively　at　residual　chlorine　of　0.5,　1.5　and　3.0　mg/L.　Moreover,　significant　nitrite　nitrogen　accumulation　appeared,　effect　of　ammonia　nitrogen　and　nitrite　nitrogen　removal　was　recoveried　after　120　and　216　hours.　Effluent　total　phosphrous　concentration　increased　when　residual　chlorine　was　up　to　1.5　mg/L　and　total　phosphrous　removal　rate　was　all　more　than　20%　after　run　for　264　hours.　Permanganate　index　was　increased　because　of　oxidation　caused　by　chlorine　and　water　purification　efficiency　was　rerecoveried　after　192　hours.