With the advent of globalization and knowledge economic era, organizations have to face an increasingly competitive business environment. With limited resources, it is imperative for organizations to allocate them effectively, to focus on potential projects, to choose high value-added projects, and to find out the proper project portfolio. The purpose of this research is to investigate the decision model and the operational mechanism of project portfolio selection for military investment and to analyze the characteristics of related projects. Finally, this research mainly proposes a decision model for project portfolio selection and the measurement of portfolio performance and develops a portfolio selection decision support system to provide a communicative platform and information for decision makers and project managers. This will improve portfolio performance, reduce the crowding out effect of organizational resources, and enhance the linkage of both project and organizational goals.