Abstract: For a simplified three-dimensional numerical model of magnetic materials, numerical simulation research of nonlinear eddy current detection signal of the modal was carried out. A simulation method and numerical code which was used to calculate nonlinear eddy current detection signal was developed based on reduced vector potential(Ar) formulation. Furthermore, relationship between nonlinear eddy current detection signal and permeability variation which was caused by plastic deformation of magnetic materials was obtained. Numerical code of nonlinear eddy current detection signal was developed. Nonlinear eddy current detection signal was calculated by numerical simulation program. Relationship between harmonic amplitude of analog signal and plastic deformation was obtained by using different initial permeability equivalent to different deformation. Comparing results of numerical simulation with experimental results, it is proved that permeability variation which was caused by plastic deformation was the direct incentive of nonlinear eddy current detection signals change.