The grounding grid is an important facility to ensure the operation of the power system. It is necessary to carry out the defect detection of the grounded flat steel in time. However, the current detection methods still have shortcomings in terms of accuracy and efficiency. The electromagnetic ultrasonic guided wave detection method can use the advantages of non-contact to realize the detection of ground nets without excavation, which has certain advantages. In this paper, a simple and effective electromagnetic ultrasonic SH guided wave transducer is designed for grounded flat steel. The mechanism of multi-physics coupling in the energy conversion process is analyzed. Finite element modeling and simulation are carried out in COMSOL Multiphysics. In order to optimize the transducer, the multi-factor and multi-level analysis are carried out according to the orthogonal test theory, and the influence of 5 parameters on guided wave excitation and the optimal parameter combination are obtained. Furthermore, a flat steel detection system is established and SH guided wave experiments are carried out. The results show that: compared with the first two parameter combinations in the orthogonal test table, the transducer performance of the optimal parameter combination increases by 14.0% and 28.6% in the amplitude of guided wave, respectively.