The strengthening of concrete structures by means of externally bonded (EB) fiber-reinforced polymers (FRP) is now routinely considered to be an effective method for enhancing the loading capacity of existing structures. However, the debonding failure often governs the behavior of FRP shear-strengthened beams and prevents them from attaining their full load capacity. This paper presents a finite element model that was developed to investigate the FRP/concrete interfacial properties on the performance of FRP shear-strengthened beams. Nonlinear behavior of the plain concrete, steel reinforcing bars, FRP composites and FRP/concrete interface are simulated with appropriate models. Once the accuracy of the numerical model is established, the numerical analysis is carried out to investigate the parameters responsible for characterizing the initiation and propagation of debonding. These are the interfacial stiffness, the interfacial bond strength and the interfacial fracture energy. In this study, the variation of load-deflection relations is considered as a basis for the comparison. Results show that the interfacial stiffness and the bond strength have neglected influence on the behavior of FRP shear-strengthened beams. Furthermore, the interfacial fracture energy is the main parameter among the bond stress-slip model parameters influencing the strengthening performance of FRP shear-strengthened beams in terms of load-deflection relations and ductility.