To address the damage identification problem of frame structures after earthquakes, a new damage identification method based on the wavelet packet decomposition was proposed.The structural vibration signal under environmental vibrations was used to constitute damage indicator (DI) as follows: the vibration signal was decomposed into each frequency band with wavelet packet decomposition, then, a damage indicator was established on the basis of the energy ratio variation on frequency domain.On the above basis, a 3D finite element model of a frame structure was created by calculating DI using the proposed method.The influence on the damage identification of different floors and different types of excitation was discussed.The results show that the DI proposed can be used to identify damage effectively and the DI value is approximately linear to the damage degree.Damage identification based on vibration signal of higher floor is better than that of lower floor and the damage identification effect with velocity signals is better than acceleration signals.