This study deals with the design of passive suspension system of railway vehicles. The proposed model has six-degree-of-freedom and can be designed via control theory. Since the classical fixed point theory is no longer applicable to the design of passive suspension system of railway vehicle, many methods have been developed to replace it. In this paper, By utilizing feedback control theories the problem is examined from the view of feedback control problem. Consequently, the “feedback gain” is a decentralized matrix composed of the suspension parameters to be optimized. Since minimizing H _∞ norm of the system implies suppressing the peaks of the magnitude of frequency response of the system, parameters optimization of passive suspension systems become a H _∞ static output feedback problems, and it is transformed to Bilinear-Matrix-Inequality (BMI) problem. One of the easiest methods to solve this BMI problem is alternative algorithm, which is derived from iterative schemes of alternation between analysis and synthesis via Linear Matrix Inequalities (LMIs). Finally, numerical simulations for the passive suspension system designed by control theory and fixed point theory will show the comparison of performance of each method.