Abstract: This paper studies the detection of artificial prefabricated defect (rectangular defect) models and the fatigue defect (triangular defect) models. A three-dimensional numerical calculation model for artificial prefabricated rectangular defects and fatigue defects was established by COMSOL multiphysics. The depth and height of the crack defects are different in detail. The relationship with the magnetic flux density Z component is discussed, meanwhile, taking the defect-free model for comparison, the differential signal of the magnetic flux density Z component is analyzed. The finite element analysis model of the eddy current testing system established by COMSOL multiphysics is used to analyze the quantitative evolution of the flux density distribution of the two different cracks with the correspond crack height and depth. Both artificial prefabricated defect and fatigue defect on the surface are considered in this research, the achieved results is useful for deeply understanding the eddy current detection principle, and also can be applied in quantitative detection of natural defects in metal components.