Pipe　wall　biofilm　plays　a　vital　role　in　water　quality　purification　in　raw　water　transportation　system　(RWTS).　This　study　investigated　the　pollutants　removal,　bacterial　community　(abundant,　rare　and　functional　taxa)　variations,　and　their　correlations　during　biofilm　development　process　under　different　pipe　materials　and　raw　water　quality.　Polyethylene　pipe　had　higher　removal　efficiency　on　ammonia　nitrogen　(NH4+-N)　and　dissolved　organic　carbon　(DOC),　while　stainless　steel　pipe　achieved　a　better　total　nitrogen　(TN)　degradation　performance.　Increasing　influent　DOC　promoted　the　removal　of　nitrogen　pollutants.　Compared　with　water　quality,　pipe　material　showed　a　greater　influence　on　bacterial　diversity　and　community　structure.　Pseudomonas　and　Planctopirus　were　the　dominant　genera　in　abundant　and　rare　taxa,　respectively.　There　were　complex　interactions　within　the　abundant　and　rare　taxa,　with　Haliscomenobacter　and　Reyranella　as　the　hub　genera,　respectively,　and　many　abundant　genera　co-occurred　with　rare　genera.　Serratia　of　abundant　taxa　and　Filomicrobium　of　rare　taxa　had　positive　correlations　with　the　influent　(NH4+-N)　and　DOC　concentration,　respectively.　Complete　ammonia　oxidation　and　ammonia　assimilatory　contributed　to　the　great　NH4+-N　transformation,　while　limited　denitrification　resulted　in　the　undesirable　TN　removal.　Functional　bacteria　and　genes　displayed　statistically　strong　correlations　with　water　quality.　Abundant　and　rare　taxa　were　significantly　affected　by　environmental　conditions　and　organic　matter,　respectively,　while　the　variations　in　functional　taxa　were　mainly　explained　by　organic　matter,　nitrogen　and　their　interactions.　These　findings　provide　novel　insights　into　the　evolution　of　abundant,　rare　and　functional　taxa　during　biofilm　development　in　RWTS,　and　highlight　their　correlations　with　water　purification　performance　and　environmental　factors.