To investigate the fatigue performance of Q420qENH welded joints after corrosion, electrolytic accelerated corrosion tests and fatigue experiments were conducted on specimens, combined with numerical simulation. A thermal-mechanical coupled finite element model was established to simulate the welding process. The fatigue life of corroded welded joints was predicted using ABAQUS and FE-SAFE by introducing residual stress fields and stress concentration factors. The results show that all specimens fractured at the corrosion pits in the middle of the weld toe. Residual stress presents tensile stress, and the fatigue life of specimens decreases significantly with the increase of fatigue stress amplitude and corrosion time. The relative errors between test and simulation results are within 15%. The S-N curves with a 95% survival rate were fitted to the fatigue data obtained from experiments and simulations, when the cycle count reaches 2 million, the maximum error between tests and sumulations is merely 4.31%, indicating small errors and good prediction accuracy. It is recommended to adjust the fatigue allowable stress amplitude category of butt joints for railway non-painted Q420qENH weathering steel to category Ⅶ in bridge design.