Fiber Reinforced Polymer (FRP) composites are widely used for rehabilitation, repair and strengthening of reinforced concrete (RC) structures. The main problem that has greatly affected the performance of flexural strengthening with Externally Bonded Reinforcement (EBR) methods is the premature debonding of FRP laminates from the beam substrate. Recently, special treatments on concrete surface prior to using FRP sheets in the EBR technique, named as Externally Bonded Reinforcement On Grooves (EBROG), has been introduced in Isfahan University of Technology (IUT), Iran. According to this method, longitudinal grooves were first caved on the tension face of the reinforced concrete beam, then the grooves were cleaned with compressed air and filled with appropriate epoxy resin. Finally, carbon fiber sheets were adhered to the surface. It is showed that by choosing specified width and height for grooves, this method can considerably postpone the debonding and in some cases may completely eliminate it. Numerical methods such as Finite Element Method (FEM) are strong ways for prediction and modeling of debonding in FRP strengthened RC beams. In this study, a novel technique (based on non-linear finite element analysis) is presented which considers behavior of the interface layer by using suitable Mixed-Mode Bond Stress-Slip models. The analyses results show good agreement with the experimental data regarding load–displacement response, crack pattern and failure mode. Also, the effects of number, width and height of the grooves, Initial flexural reinforcement ratio and number of FRP layers on the behavior of the EBROG method are investigated. The results indicated that by choosing appropriate number and dimensions for grooves (depending on internal and external reinforcement ratio), this method can control the premature debonding of FRP laminates. Finally, based on these parametric studies, some technical suggestions and design diagrams are presented. Key Words FRP Materials, Debonding, EBROG Method, FE Method, Interface Layer