Abstract
This paper introduces a simple and approximate method of calculating the intersections on the cross section of the torus crossed by a torus magnetic field line, which is added by a weak perturbed field. The method is based on consideration of the interpolation of the values of transition tables of the position of starting points and arrival points of magnetic field lines. Simplified geometry model is used to clarify the idea of the method. The calculation program is parallelized to implement on HITACHI SR-220l parallel computer to reduce the calculation time. Some numerical results are presented