Microbiologically induced corrosion (MIC) is known as one of the most damaging failures for pipeline steels. Especially, sulfate-reducing bacteria (SRB) is the most widespread strains in soil and seawater environments and is the typical bacteria associated with MIC. SRB may cause severe localized attack, leading to pipeline failures in forms of pitting, crevice corrosion, dealloying and cracking. In this work, SEM, Raman spectroscopy, XPS, scanning vibrating electrode (SVET) technique, EIS and other electrochemical techniques were used to study the formation of SRB biofilm, its electrochemical interaction with X80 pipeline steel and corrosion behavior of the steel in a simulated seawater. The results showed that barrier effect of the extracellular polymer substances (EPS) inhibits corrosion process of X80 steel in the initial formation of EPS and SRB micro-colony. After the formation of SRB biofilm, open circuit potential (E_OCP) of the steel decreases 20 mV, and SRB significantly promotes the corrosion process of the pipeline steel. In the later stage, due to SRB and its biofilm, the corrosion rate of X80 steel exposed in SRB inoculated environment is almost one order of magnitude higher than that in the sterile environment. The biofilm have complexation effect and chelation effect with corrosion products (Fe²⁺/Fe³⁺). SRB cells, metabolites and biofilms have direct and indirect electron interactions with the steel substrate. These various coupling effects promote occurrence and development of local corrosion on the surface of the steel beneath biofilm.