The edge of material loss is crucial for material loss evaluation. Lamb wave tomography and model-based edge detecting have been used in isotropic media. Time of flight and velocity of lamb wave are ultrasonic signal features to reconstruct the edge map of material loss. The correlation technique is employed to get the time of arrival more accurate. An ellipse model is used to represent the defects with apparent directional property, and edge detecting will be realized by it. The reconstructed map shows clearly that edge detecting method in this paper is efficient for material loss detection.