Aiming at the problem that the ultrasonic Lamb wave excited by the electromagnetic ultrasonic transducer ( EMAT) has multiple modes, a method is proposed to excite a single mode of the Lamb wave by optimizing the structure of the transducer. First, according to Biot Savart‘s law and Maxwell′s equations, the relationship between the shape of the permanent magnet and the magnetic field distribution is studied, and a new type of magnetizable “arch bridge” permanent magnet structure is designed. Then, the simulation experiment and the actual measurement experiment were performed on the EMAT before and after the optimization. The experimental results show that the S0 modal amplitudes of the Lamb wave excited by the EMAT after optimization are 1. 05 and 1. 1 before the optimization, and the A0 modal amplitudes are respectively It is 0. 22 and 0. 12 before optimization; the ratio of S0 mode to A0 mode is also increased from 2. 60 and 1. 82 before optimization to 12. 48 and 16. 17 respectively. It can be seen that, compared with the ordinary EMAT before optimization, the optimized EMAT can excite the S0 mode and suppress the A0 mode well, thus verifying that the new EMAT can effectively excite the single S0 mode of the Lamb wave.