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The effect of ORP (oxidation–reduction potential) on the bacterial community and corrosion rate was investigated in this study. A continuous sulfate-reducing bacteria (SRB)-enriched reactor equipped with an ORP controller was operated from anaerobic to anoxic condition in this bio-corrosion experiment for over 200 days. Testing mild steel coupons were placed into the reactor for immersion test which was used to compare with the result of electrochemical corrosion current density. The results showed that as the ORP increased, the sulfide, corrosion current density and the proportion of SRB in microbial community would decrease. This study employed oxygen to change the microbial communities, which successfully enabled heterotrophs to inhibit SRB even under excessive TOC and sulfate inflow conditions. However, from the results of corrosion weight loss it could be discovered that the fact of higher control of ORP leading to better corrosion inhibition was not certain. Once the ORP was controlled to −250 mV, the same result could be achieved as well as the ORP being controlled to −180 mV. In addition to the advantage of energy-saving, controlling ORP at −250 mV can also prevent more corrosion reactions from possibly being caused by other microorganisms in the continuous rising of ORP.