Abstract: The corrosion of carbon steel in enriched anaerobic bacteria which including sulfate-reducing bacteria(SRB) and iron-reducing bacteria(IRB) was studied by means of electrochemical impedance spectroscopy.The results showed that the mixed anaerobic biofilm inhibits corrosion of carbon steel.The activity of IRB was considered to be the reason for initial corrosion inhibition and iron phosphate and green rust may play an important role in inhibition of the corrosion under the influence of mixed anaerobic biofilm.