1. A computer system, comprising: a central processing unit; a storage device storing one or more programs, the one or more programs comprising: an acquisition module configured for reading a data file corresponding to N-port network system format in a storage device, and obtaining S-parameter matrixes from an N-port network system; a parameter check module configured for checking if all S-parameters in the S-parameter matrix satisfy passivity, and performing an interpolation algorithm to supplement S-parameters with passivity when some S-parameters not satisfy passivity; a function generation module configured for generating numbers of pole-residue, times for recursion and a tolerant system error of a rational function that is a function for determining the S-parameters in the S-parameter matrix; and an equivalent circuit generation module configured for generating a rational function matrix composed with S-parameters by performing a vector fitting algorithm based on the numbers of pole-residue, and generating an equivalent circuit compatible with HSPICE format based on the generated rational function matrix.