In this paper the existing methods of strengthening for reinforced concrete beams were introduced and also using ANSYS structural software, reinforced concrete beams strengthened with external unbonded reinforcements were modeled and analyzed nonlinearly to determine their ultimate flexural strength and deformability. For this purpose, 24 beams with different dimensions and different properties were modeled, analyzed and compared with the experimental results. The effect of different parameters, such as percentage of internal reinforcement, shear span to effective beam depth, the existence of deflectors to hold in place external reinforcement, span length to effective beam depth ratio, and the percentage of external reinforcement on the ultimate flexural strength and deformability we re studied. The results of the analysis show that increase in shear span to effective beam depth ratio, will cause a decrease in the external reinforcement force, flexural strength and deformability of the beam. The use of deflectors for external reinforcement will decrease deformability but increase flexural strength of the beam. Increasing percentage of internal reinforcements will decrease both the force in external reinforcement and deformability of the beam. In spite of the decrease in deformability due to the usage of external unbonded reinforcement for strengthening of reinforced concrete beams, the method can be safely used for flexural strengthening of reinforced concrete beams. Finally the model introduced in this research can be properly used for the analysis of the beams strengthened by external unbonded reinforcement.