Abstract: Detect the crack defects in the lap area of a double-layer steel plate, considerate the influence of steel cladding and weld surround on the detection signal, a method is proposed to detect crack defects by taking advantage of the SH0 mode guided wave without frequency dispersion. Based on the Comsol multi-physical simulation platform, a three-dimensional structure model of double-layer steel plate was established, and the crack defects of different lengths were constructed in the lap area. The results show that the defect echo signal is the same as that without the defect when the detection wavelength is 12.8 mm and a crack defect length is 10 mm, noise signals are largely overlapping and cannot be detected. As the length of the crack defect varies from 10 mm to 40 mm, the longer the crack defect is, the more pronounced the echo signal is. The error between the calculated position and the actual position is 1.79%. This study provides a theoretical basis for the online detection of defects in the lap area of double-layer steel plates.