The work aims to discover the role of SRB in crack initiation of pipeline steel. The elastic and plastic stresses were applied via a constant-load set-up. The components of corrosion products were detected by XPS and EDS. The biofilm morphologies and the corrosion morphologies of pipeline were observed by SEM to study the initiation and propagation of mi-cro-cracks of pipeline steel under elastic and plastic stresses. Elastic and plastic stresses had no significant effect on SRB growth. Regardless of the actions under elastic stress or plastic stress, the SRB physiological activities changed the structure and increased the sulfur content of corrosion products and enhanced the local corrosion sensitivity of the steel. The synergistic effect of plastic stress and SRB, had greater influence on the initiation and propagation of micro-cracks in the steel compared with that of elastic stress and SRB. Under the action of plastic stress, micro-cracks bifurcated on the pipeline steel in both the sterilization and SRB-inoculated soil solutions. Both the elastic and plastic stresses can promote the corrosion process of the pipeline steel. The bacteria assisted cracking becomes more severe under the action of the plastic stress. The micro-crack propagation of the steel is related to the physiological activity of SRB.