This research presented the damage identification problem of frame structure using the wavelet transform of strain mode. Solving strain modal parameters of plane frames with cracks by means of the finite element theory, applying the gauss2 wavelet transform to analyze the stain mode of plane frame, and denoising the wavelet coefficients of the strain mode by db3 wavelet, then the location of crack of the plane frame could be identified by the maximum of wavelet coefficients after denoising. Taking one-layer plane frame as an example, this research gave the finite element model of framework with sheet crack (non-through surface crack and internal crack), calculated the strain mode of the structure, and identified the location of cracks by wavelet analysis of strain mode. Results show that this method is able to identify the damage of frame structure. Numerical calculation shows that the approach is effective. This paper provides a valuable reference of structural damage identification and diagnosis in engineering applications.