In simulation of a charged particle's guiding-center orbit in Tokamak equilibrium configurations, an efficient way to build physical functions such as magnetic field was obtained. Discrete Fourier transform is applied to replace cubic spline interpolation and B spline interpolation methods in calculation of gulding-center's trajectory. It has same accuracy as cubic spline interpolation and facilitates calculations in tearing mode as well. The method holds naturally property of symmetry. Derivatives of 3rd order or above can be obtained easily. Moreover, effect of incorrect data is reduced to the minimal limit compared with cubic spline interpolation.