As the life age of the existing structures are required to meet the changing demands on civil infrastructures. So strengthening and retrofitting are required. Recently many techniques to strengthen the reinforced concrete beams in flexural by using fiber reinforced polymer (FRP) had appeared. The most famous technique among them is strengthening the (RC) beams with externally bonded FRP sheet to the tension side of the beams. So this paper presents numerical simulation of the structural behavior of reinforced concrete beams strengthened with externally bonded FRP sheet by using (2D) rigid body spring model (RBSM). A non-linear RC beam model with bond-slip relations between the concrete and steel reinforcement plus concrete and externally bonded FRP sheet had been used. Comparisons were made between the experimental and analytical results. In general there was good correlation between the experimental results and non-linear RBSM model results.