Abstract: The mechanical models for reinforced concrete (RC) , cementation layer and steel plate of externally bonded RC beams are set up by using corresponding constitutive models and different types of finite elements. The integral performance of the beam and stress of the cementation layer is analyzed. It can be seen that the stress is comparatively great at both ends of the plate along the beam's length, while the thickness of the cementation layer has a little influence on the shear stress of the cementation layer and the integral performance of the beam.