Abstract: A modefied Newton-Raphson method is presented in this report. It consists of introducing relaxation factor ω, parameter α into general Newton-Raphson method. In convergence process, physical variables are updated reasonably in physically meaningful range, so they smoothlly converge to a solution. Examinations were made with nonideal distillation system. The results showed that the present method gave better convergence character than either Newton-Raphson or successive substitution approach.