The method for damage identification based on wavelet packet component energy is sensitive to structural damage. In order to select the characteristic frequency band more efficiently, the method in the point of frequency band decomposition of wavelet packet transform is analyzed. The structure vibration response is transformed by wavelet packet and the component energies are calculated. The frequency of the response and the range of each frequency band are analyzed. The frequency band, in which the main frequency of the signal exists, and the adjacent bands are selected as the characteristic bands. If the frequency of the signal changes, the energies of the characteristic bands change more greatly than the frequency itself. When the structure is damaged, the frequencies of the response on impulse force change and the change of WP-based component energies are used as the indices of the damage. A dynamic test on a reinforeced concrete beam confirms the feasibility of the method.