It is very important to analyze the vibration characters and to identify the damage of cracked structures. In this paper, the effects of a transverse surface crack on mechanical impedance of simple supported cracked beams are investigated. A method for damage identification based on mechanical impedance characters is proposed in this paper, which makes use of the driving-point mechanical impedance characteristics of the cracked beams stimulated by harmonic force. The proposed impedance method is used to characterize the local discontinuity on account of cracks, and a rotational spring model is proposed to model the crack. Subsequently, the proposed method is verified by a numerical example of a simply supported beam. Combined with the information of first resonance frequencies, the proposed method can identify the presence of the crack and localize the crack, and the disciplinarian of driving-point impedance change is investigated when the depth of cracks is varying, and the extent to the crack damage is qualitatively identified.