The Korean government has operated various mega-development projects in order to help nation progress into the future. However, many problems and concerns have been raised on the mega-projects` delay and failure in South Korea. Moreover, there are many technical and executive problems; such as trial and error of development work, failure of validity test, complicated decision-making processes, and so on. With these concerns and problems to mega-development projects, finding a sustainable development from mega-projects is becoming a new issue in the field of mega-development projects. Therefore, the main purpose of this study is to investigate whether or not most mega-development projects conducted by the government exactly corresponds with sustainable development (such as environmental soundness, economic efficiency and social equity) focusing on Saemangeum project. Using causal loop analysis, this study gives some significant results to us. First, for environmental soundness, both central and local government should ensure water-purity control system for farming, industry, leisure, and others. Second, for economic efficiency, both governments not only have to secure a budget for completion of infrastructure of the Saemangeum project but also support financial assistance to Saemangeum project. Third, for social equity, three local governments i.e., Gunsan, Gimje, and Buan) should stop debate and conflict with regard to an administrative district of Saemangeum region. Finally, most politicians should not use Saemangeum project for political means. Rather, they should recognize the project as a motive power for economic development of Jeollabukdo.