The objective of this present research is to propose a simplified analytical and numerical approach to predict the interfacial stress of simply supported reinforced-concrete beams reinforced with prestressed carbon fiber-reinforced polymer composite plate. Analytical design methodology is based on equilibrium and deformations compatibility requirements in and all parts of the strengthened beam, i.e. the concrete beam, the prestressed carbon fiber-reinforced polymer plate, and the adhesive layer. The results show that there exists a high concentration of both shear and normal stress at the ends of the laminate, which might result in premature failure of the strengthening scheme at these locations. In numerical analysis, the mesh sensitivity test shows that the finite element results for interfacial stresses are not sensitive to the finite element mesh. The finite element analysis then is used to calculate the interfacial stress distribution and evaluate the effect of the structural parameters on the interfacial behavior. Numerical results from the present analysis are presented both to demonstrate the advantages of the present solution. This research is helpful for the understanding on mechanical behavior of the interface and design of the interfacial stress in reinforced-concrete beams reinforced with bonded prestressed carbon fiber-reinforced polymer plate.