Abstract: In this paper, Lamb wave transducers are studied in terms of Lorentz force mechanism and magnetostrictive force mechanism, in order to increase the transduction efficiency of electromagnetic ultrasonic Lamb wave transducer in the process of tank bottom steel plate detection. Based on theoretical research, the square of static bias magnetic intensity of sheets is proportional to echo signal strength. Finite element simulation calculation is conducted on tank bottom plate Q235. The distribution of time mean of particle energy density inside steel sheets is investigated by changing the structures of permanent magnets in electromagnetic ultrasonic Lamb wave transducers. Then experimental study is launched on Lamb wave transducers. It is shown that steel plate detection distance of Lamb wave transducers rises by 2.42 times after its structures of permanent magnets are changed.