Based on the scaled boundary finite element method, the propagation behavior of Lamb waves in a plate encountering multiple cracks, built-in vertical and transverse cracks, and depression was simulated. Different cracking angles, depths of the built-in crack and curvatures of pit were simulated under the A₀ and S₀ excitation mode, in which the mode amplitude of the reflected wave were analyzed. On the same plate, different crack pattern will have different increment for the waveform. The mode amplitude of the reflected wave increases with the increase of the crack depth and the crack angle. As the cracking angle of built-in crack increases, the effect of the mode amplitude in reflected waves is more obvious when the excited mode is antisymmetric A₀ mode. The mode amplitude in the reflected wave decreases as the depression on the plate slows down, which is more obvious when the excited mode is symmetric S₀ mode.