Based on the fatigue constitutive models of concrete and steel reinforcement, as well as the bond-slip constitutive model of the FRP-concrete interface under fatigue loading, a finite element model of reinforced concrete (RC) beams strengthened with externally bonded fiber reinforced polymer (FRP) under fatigue loading was established using ABAQUS. The model simulated the characteristics of the flexural fatigue life of FRP-strengthened RC beams influenced by the interfacial bond performance. A fatigue life prediction formula for FRP-strengthened RC beams that simultaneously considered the effects of steel reinforcement stress amplitude and FRP axial stiffness was proposed. The results indicat that the finite element model considering the interfacial bond performance can more accurately simulate the fatigue failure modes of FRP-strengthened RC beams. Reducing the stress amplitude and increasing the FRP axial stiffness can both enhance the flexural fatigue life of FRP-strengthened RC beams to varying extents. The results of the prediction formula are in good agreement with the experimental data, thereby verifying the accuracy of the formula and providing a valuable reference for practical engineering applications of FRP-strengthened RC beams.