A simulation system and method for generating equivalent circuits compatible with HSPICE reads data corresponding to N-port network system format in a storage device, and obtains S-parameter matrixes from the N-port network system. S-parameters in the S-parameter matrix that satisfy passivity are checked, and an interpolation algorithm to supplement S-parameters with passivity when some S-parameters not satisfy passivity is performed. Numbers of pole-residue, times for recursion and a tolerant system error of a rational function are generated for determining S-parameters. A rational function matrix composed of S-parameters is generated by performing a vector fitting algorithm, and an equivalent circuit is generated compatible with HSPICE format based on the generated rational function matrix.