Abstract: To investigate the residual fatigue performance of stay cable wires with corrosion-fatigue damage after long-term service, fatigue tests were conducted on real bridge wires with 21 years of service in Hunan Province and 7 years of coastal service in Guangdong Province. The wires were divided into three groups (B₁, B₂, B₃) according to corrosion severity. A three-parameter Weibull distribution was adopted to fit S-N curves. Combined with fracture morphology and crack propagation area, the influence laws of corrosion damage, of cumulative fatigue damage and, of stress ratio on residual fatigue performance are revealed. Test results show that the fatigue resistance of stay cable wires after long-term service decreases significantly due to corrosion and fatigue damage. Once the wire matrix is corroded, the existing corrosion damage degree becomes the dominant factor affecting the residual fatigue performance. Cumulative fatigue damage reduces the toughness of long-serving wires, leading to a sharp reduction in the crack propagation area and the disappearance of the fatigue limit. A high stress ratio significantly shortens residual fatigue life and increases the dispersion of fatigue life. Cracks of long-serving stay cable wires mostly initiate from surface corrosion pits. The crack propagation area decreases with the increase of damage degree, and a high stress amplitude is more likely to induce multiple crack sources in corroded wires. The study indicates that the standard design fatigue strength should not be directly applied to the residual fatigue life prediction and to operational safety assessment of in-service stay cables. The residual fatigue strength should be reasonably determined by the basis of the actual service conditions of the cables.