Abstract: This paper studies nondestructive testing method of locating defect in thin plate-like structure based upon the active lamb wave detecting technique with the aid of laser vibrometer. In the experiment, lamb wave is actuated by single piezoelectric transducer (PZT) and received by laser vibrometer. Firstly, the propagation property of lamb wave in thin steel plate was explored, the relevant dispersion curves were drawn, and finally the experimental actuation parameters were optimized. By integration of elliptic imaging theory and probability imaging algorithm, it is effective to get two-dimensional images of defect in plate-like structure from signals received by omnidirectional multi-sensor array. The result shows that this kind of nondestructive method can locate man-made damage and get two-dimensional images of defect in an effective way.