Dynamic analysis is conducted for a cracked beam with imperfectly bonded piezoelectric patches using the finite element method in the paper. The property of adhesive between the PZT patches and the host beam is taken into account based on the peel stress model as well as the shear lag model and thus the three-dimensional (3D) model of piezoelectric patch-adhesive-host beam coupled system is developed. Based on the established three-dimensional EMI model, the effect of some physical parameters such as vibration mode of main structure, the mass of adhesive layer and crack depth etc. on electromechanical impedance signatures is investigated. Finally, the root-mean-square deviation (RMSD), a kind of non-parametric damage index, is also employed to identify the damage severity of the cracked beam.