Optimization and dynamic reliability analysis of the structural system are combined. A methodology of optimum design based total failure probability of the structural system with multi-degree freedom under stationary stochastic excitation is presented when minimum weight of the structure determined by design parameters is the objective function. According to the spectrum analysis theory, the statistical property of the response of structural system under stationary random excitation is analyzed. At the same time, Possion process model based on first passage failure is used to calculate the reliability of the structure, and the optimum design parameters are finally obtained through Hestenes-Powell (HP) method. The result of evaluated examples demonstrates that the method presented in this paper is effective.