Abstract: In order to study the fatigue performance of Q345C structural steel commonly used for bridges after corrosion damage, the electrochemical accelerated corrosion test and tensile fatigue test of Q345C steel were carried out. The distribution characteristics of corrosion pitting depth and fatigue life of Q345C steel under different corrosion damage levels were obtained, the S-N curves under 50% and 97.7% survival rates were given, and the fatigue fracture characteristics of specimens with different corrosion rates were compared and analyzed. The fatigue life simulation analysis was carried out by 3D scanning reverse modeling combined with ABAQUS/FE-SAFE. The results show that with the increase of corrosion rate, the corrosion area changes from pitting corrosion to uniform corrosion; The reduction of fatigue performance by corrosion is related to the stress level, especially at low stress level; The S-N curve of 97.7% survival rate of non-corroded specimens is close to that of BS 7608 and slightly larger than that of GB 50017−2003, while the S-N curve of 97.7% survival rate of corroded specimens is lower than that of common fatigue codes, and the equivalent fatigue strength of 2 million cycles is significantly reduced; There are obvious fatigue steps on the fracture surface of the corroded specimen, and the plastic deformation is small after fracture; The crack growth area ratio of the fracture surface of the specimen is inversely proportional to the stress level and corrosion rate; The maximum error of fatigue life simulation results of corroded specimens is only 6.32% compared with the test results.