The early damage detection of large structures is very important to prevent the disaster due to its global failure. In this paper, a crack detection method of the beam-analogy structure based on the wavelet transformation of mode shape is presented. The method can effectively detect the singularity of mode shape caused to the inconsistency of bending moment and shear force at the damaged part using the discrete wavelet of mode shape and its inverse transforms of detail components. To investigate the validity and the applicability of the presented damage detection method, numerical simulation and experiment are carried out for the idealized beam and the real ship structures.