The composite fiber materials of polymers (FRP) have physical properties, which are exploited recently for the reinforcement and rehabilitation of the structures, in mechanical, civil engineering and biomedical field, subjected to degradation or default risks. Since a beam without any form of reinforcement will fail when subjected to a relatively small tensile load. Therefore the use of the FRP to strengthen the structures is an effective solution to increase the overall strength technique. In this paper, a new theoretical approach model to estimate shear and peel-off stresses is proposed. Axial stresses and bending moment coupled with shear deformation and thermal effect in an FRP-strengthened beam are considered, including the variation in FRP plate fiber orientation.