By means of the wavelet analysis theory, the damage identification of elastic plate was studied. Adopted the finite element method to analyze the dynamic character of the plate and applied the method of Lanczos for calculating the strain mode, and the strain mode is analyzed by mexh wavelet (Mexican Hat wavelet). The location of the declining stiffness is identified by the place where maximum of wavelet coefficients appears. Therefore, this method is applied to the elastic damaged plate. Three types of damaged regions in rectangular simply supported plate are recognized, which indicates this method is effective and accurate. And this method has a certain value in the project application.