Abstract: The formation of defects on the surface of submarine pipeline due to corrosion is quite easy, and this kind of defect is characterized by large geometrical depth, rapid propagation and difficult detection and brings great potential risks to pipeline accidents. In this paper, the shielding effect on the cathodic protection by the interior of defects when there were corrosion defects in the surface of X80 steel submarine pipeline was investigated by means of numerical simulation. And local potential and anodic/cathodic current density at the defects were simulated by virtue of finite element method. It is indicated that the cathodic protection current is partially shielded at corrosion defects, especially at their bottom. And the shielding effect on the cathodic protection at defects is increased with the increase of defect depth and the decrease of defect width. The research results provide the guidance for estimating on-site corrosion status and remaining life of submarine pipelines.