Abstract: In order to realize the nondestructive testing of the defects of variable cross-section plates, the propagation characteristics of SH guided wave in variable cross-section plates structure are simulated and experimentally studied. Finite element software is used to investigate the effect of variable cross-section and weld on the propagation characteristics of a SH guided wave. At the same time, the guided wave detection experiment is carried out on the variable cross-section plates, and the influence of SH guided wave propagation characteristics on defect detection ability is analyzed. Experiments are conducted to detect defects in variable cross-section plates, and the effects of defect variations at different depths on the detection signal is analyzed in the time and time-frequency domains. The findings show that when the SH guided wave propagates in the variable cross-section plate, the mode conversion occurs, and the number of modes will also be affected. Propagation of SH-guided waves in a variable-section plate with welded seams, the presence of welded seams in the variable cross-section plate does not affect the mode conversion and the number of modes of the SH guided waves. For defects located behind the weld, SH guide wave can also achieve the detection of defects, and the detection sensitivity of high-frequency SH guide wave is higher. The results of the finite element simulation are consistent with the experimental results, demonstrating that the model can accurately assess the flaws in the variable cross-section plate and its significant potential for use in engineering.