This paper numerically investigated the guided wave propagation along the reinforcing rebar in reinforced concrete structures. The finite element analysis was conducted to demonstrate the multi-mode and attenuation characteristics of guided waves in reinforced concrete structures, where the influences of thicknesses of concrete cover were also considered. The phenomenon of wave conversion resulting from interface debond between reinforcing rebar and concrete was specifically considered. It shows that the guided waves propagating in the integrated and debonded regions exhibit disparate behaviors in terms of the mode, group velocity and attenuation characteristics. The results indicate that the interface debond length can be determined by the amplitude and spectrum characteristics of the received waveform.