FEM analysis is commonly used in wide range of industrial design works such as machine design, aeroplane design. There are some experimental studies about the application of FEM combined with optimization methods in order to accommodate complicated mutuary related phenomenon or to accomplish optimization automatically. In this study, optimization methods, FEM and design code inspection program are linked together to automatically seek and generate optimum structural dimension for objective steel bridges. It is discussed that Possibility of conversion of design method from traditional beam theory design to FEM based design where three dimensional structural behavior are easily considered.