The flow velocities and pipe materials may be variable in drinking water distribution system, and their interaction on the water quality and biofilm formation under a certain chlorine level have been investigated. Heterotrophic plate counts and denaturing gradient gel electrophoresis were employed to analyze biofilm formation, and the results showed that the chlorine, TOC of bulk water, total bacteria counts and microbial community structure were all varied in pipe materials, while flow velocities only affected the chlorine of bulk water and biofilm biomass. In the same time, PE pipes attached significantly greater biofilm biomass than stainless steel. The biofilm biomass grown under flow velocities 0.2 and 0.4 m／s were significantly greater than that under 0.8 m／s, but the biofilm growth between 0.2 and 0.4 m／s were not significant. In the mature biofilm microbial community, Sphingomonas sp. and Bacillus sp. were dominant in all biofilms, while the hydrophobic bacteria were difficult to grow on the stainless steel pipe, especially under high flow velocities.