Abstract: In order to overcome the instability of manual detection and obtain the preservable detection results, this paper studies the automatic detection method of Lamb wave for thin sheet metal. The automatic detection by Lamb wave is realized by adding the simulation manual detection method of Lamb wave scanning device on the basis of C-scan detection equipment in water immersion. The stability and other properties of the 4. 5 mm thick plate standard test block were tested. The results show that the automatic detection method can obtain stable test results.