Microbiologically corrosion is a critical factor contributing to the degradation of marine engineering infrastructure.Electrochemical methods and slow strain rate tensile(SSRT) tests were employed to evaluate the effect of cathodic protection (CP) on the corrosion behavior of X70 pipeline steel in marine environments containing sulfate⁃reducing bacteria (SRB).Together with microstructural characterization,the stress corrosion cracking(SCC) mechanism of X70 steel in SRB⁃containing marine environments was analyzed.The results indicate that CP potentials of -0.775,-0.850 V promoted SRB growth.When the CP potential reached -1.000 V,it not only promoted the proliferation of SRB but also accelerated their transition into the decline phase.In the absence of applied stress,the optimal CP potential for X70 steel in SRB⁃containing marine environments was -0.850 V.Without CP,the SCC mechanism of X70 steel was a hybrid mode involving anodic dissolution induced by the marine environment and hydrogen⁃induced cracking caused by SRB.At CP potentials of -0.775,-0.850 V,the SCC mechanism was dominated by SRB⁃induced hydrogen⁃induced cracking.When the CP potential was -1.000 V,the SCC mechanism was a hybrid mechanism jointly induced by anodic dissolution caused by the marine environment and hydrogen⁃induced cracking induced by the CP potential.The synergistic effect of SRB and CP significantly increased the hydrogen embrittlement susceptibility of X70 steel in marine environments.