In order to investigate the performance degradation law of concrete beams under the long-term influence of multiple factors such as corrosion, fatigue, and creep, orthogonal grouping experiments involving corrosion, fatigue, and creep were conducted on 21 test beams. Measurements and calculations were performed on the corrosion depth of the steel reinforcement, the stiffness of the beams, and their fatigue life. The research results indicate that, compared to undamaged beams, the corrosion depth in damaged concrete beams increases by 1.337 to 1.934 times under 2.5%, 15.0% and 60.0% fatigue life ratios and 3 and 6 months of sustained loading. As the degree of reinforcement corrosion and fatigue damage deepens, the stiffness of the damaged beams decreases by 1.694 kN·m2, and under sustained loading, their stiffness is only 34.1% of that of the undamaged beams. After the combined effects of corrosion and creep, the fatigue life of the damaged beams is reduced to only 16.14% of that of the undamaged beams. Based on the experimental results, critical corrosion depth attenuation coefficients, short-term stiffness reduction coefficients, stiffness degradation coefficients, and fatigue life attenuation coefficients for damaged concrete beams are provided, reflecting the impact of complex loading and environmental factors on the long-term performance of concrete beams. These findings offer a scientific basis for the long-term performance assessment of concrete structures.