This paper presents a numerical study of wavenumber change of guided wave in TPS with debonding by using Local wavenumber method. The results show that the wavenumber of guided wave in TPS debonding region is smaller than that in TPS bonding region. Furthermore, the influence of thickness and elastic modulus of TPS adhesive layer on the wavenumber is also considered. The results show that the increase of elastic modulus and thickness will lead to the decrease and increase of wavenumber in TPS bonding region, respectively. Finally, the wavenumber variation characteristics of guided wave in TPS with debonding are used to identify the debonding of different sizes in TPS. The results show that each debonding can be identified, which proves the feasibility of using local wavenumber method to identify the debonding of TPS.