Abstract: In depth detection of surface cracks, this paper uses numerical simulation methods to compare the surface detection method and upper surface detection method of dual-source. The results show that the probe acts on the upper and lower surfaces can be detected on the upper and lower surfaces. Comparing the two detection methods, the lower surface detection method is easier to implement. For defect detection of 0.5 mm to 2.5 mm, the lower surface detection method has a maximum of 25.1%, while the upper surface detection method has a crack depth measurement error within 2.5%, In contract, the detection accuracy is higher.