Abstract: Based on the coherence function and effective frequency band of hammer excitation,the frequency band of the frequency response function was determined. Then the imaginary part of frequency-response function and the information entropy theory were combined to calculate the singular value entropy of Hankel-matrix which was constructured by the imaginary part of the frequency-response function. Finally, probabilistic method was used to calculate the abnormal condition and examine the internal defects of concrete. Based on these, the paper offers a simple and practical method of qualitative analysis to image the concrete defect. Firstly, the specimen was divided into two zones to differ in degree of defect.Then the projection function value of the defect cell was calculated and the non-defect cell was set to zero.Lastly, the inside situation of concrete was reacted by the contour of the projection function,and the test was performed to assess availability of the method.