Abstract: The bending fatigue performance of Q345 steel single-sided corner joints was tested. Fatigue life data under different stress levels were obtained through loading tests, and the crack initiation and propagation behaviors were analyzed to reveal the failure mechanisms of the joints under cyclic loading. The results show that as the stress level rises, the fatigue failure location of the welded joints shifts gradually from the weld root to the weld toe, demonstrating a clear failure location migration phenomenon. Further microstructure analysis shows that this phenomenon is mainly influenced by the local strength variation of the material and stress concentration distribution changes caused by micro-defects in the weld. To achieve a reasonable evaluation of the fatigue life of corner joints, fatigue life prediction and comparative analyses are performed based on experimental results using the notch stress method and structural stress method, respectively. The results show that the structural stress method offers better prediction accuracy across different stress levels, with predicted fatigue life data falling within twice the life scatter band, outperforming the notch stress method. This validates the applicability and reliability of the structural stress method in fatigue life assessment of welded joints.