AbstractAs a widely used deck system of long-span bridges, the U rib–diaphragm connection in orthotropic steel bridge deck (OSBD) is prone to fatigue cracking under repeated vehicle loads, and the corrosion medium will accelerate the fatigue cracking. To study the influence of corrosion on the fatigue properties of bridges and the fatigue crack propagation law, the three-dimensional (3D) corrosion morphologies of typical OBSD components under different mass loss rates (w) were obtained by the cellular automata (CA) corrosion model. The, the CA model could reflect the electrochemical metal (Me) corrosion. Then, based on AutoCAD, Rhinoceros, and ABAQUS, the solid model of a U rib–diaphragm connection with surface pits was obtained in ABAQUS. Finally, a multiscale finite-element (FE) model of a long-span bridge with millimeter-scale corrosion pits and cracks was established. The stress intensity factors at crack tips and dynamic fatigue crack propagation at the U rib–diaphragm connection were studied by the extended finite-element method (XFEM), and the difference in fatigue crack propagation life and cumulative energy release rate under different wwere investigated. The results showed that compared with the method of uniform thickness reduction to characterize corrosion effects, the ultimate bearing capacity that was obtained by the CA corrosion model was more consistent with the experimental results. Compared with when the corrosion effects were not considered, when the wof the U rib was 6%, 8%, and 10%, the peak stress intensity factor (KI) of the crack initiation at the weld toe of the U rib increased by 32%, 49%, and 86% and the fatigue growth life of the U rib–diaphragm was reduced by 6.5%, 18.9%, and 50%, respectively. According to the cumulative energy release rate of the crack initiation at the weld toe of the U rib, the crack was a composite crack that was dominated by the opening model crack, supplemented by the in-plane shear model crack and the antiplane shear model crack.