Study　on　formation　process　of　biological　purification　efficiency　in　raw　water　delivery　pipelines　was　beneficial　to　improve　water　quality　in　long　distance　raw　water　delivery　pipes.　Using　simulated　pipeline　reactors　to　simulate　water　situation　in　raw　water　delivery　pipelines,　and　water　samples　were　prepared　in　laboratory.　The　influent　and　effluent　water　quality,　the　microorganisms　in　the　biofilm　is　continuously　monitored.　Results　show　that　the　ammonia　nitrogen　(NH4+-N)　and　organic　matter　removal　are　stabilized　after　a　gradual　increase　in　first,　and　stable　value　decreases　slightly　compared　to　the　maximum　in　the　formation　process　of　biological　purification　efficiency.　Biofilm　grow　on　polyethylene　slides　in　simulated　pipeline　reactor　and　then　harvest　within　45　days,　the　removal　rate　of　NH4+-N　remains　stable　at　75%.　Nitrite　nitrogen　(NO2--N)　effluent　concentration　remains　stable　at　0.02　mg/L.　Ammonia　oxidizing　bacteria　(AOB)　is　dominant　strain　compared　to　nitrite　oxidizing　bacteria　(NOB)　in　raw　water　delivery　pipes.　Removal　rate　of　UV254　and　turbidity　are　about　30%,　and　orthophosphate　(PO43-)　removal　rate　ranges　from　13.64%　to　38.78%.　©,　2014,　Harbin　Gongye　Daxue　Xuebao/Journal　of　Harbin　Institute　of　Technology.　All　right　reserved.