Corrosion,one of the most common problems of metal pipe for water supply,generally leads to poor water quality,bacteria proliferation,water capacity decrease and other problems.As microorganisms affect corrosion by changing the characteristics of metal surface,the mechanism of microbial corrosion still remains unclear.The corrosion behavior of ductile cast iron is implemented in the dynamic flow and static conditions,in which variations of water quality and microbial community are analyzed in details.The results show that if the corrosion rate of ductile cast iron decreases,the corrosion of cast iron will result in a lower DO and a higher total iron in bulk water.The number of microorganisms is not a decisive factor of corrosion,even though the counts of bacteria had a close relationship with DO.On the basis of the detection of the 10 kinds of nitrate-reducing bacteria by Miseq sequencing,NRB of the biofilm biomass accounts for 18.3％ on the 30th day and 20.5％ on the 55th day.Even though aerobic NRBs go into the biofilm later than the facultative anaerobic NRBs,the growth of the anaerobic NRBs is not affected.