Abstract: The South China Sea has long been regarded as an important strategic position linking the Pacific Ocean and Indian Ocean, and a resources-abundant region with oil and natural gas deposits. Integrating and sharing of multi-source marine environmental data are needed to support status analysis and decision making in the South China Sea. Through analyzing the related theories and technologies of marine geographical information systems (MGIS) at home and abroad, this paper designs and implements a prototype system based on the service-oriented architecture (SOA), and is called South China Sea Geographical Information Decision Making Simulation System. The system integrates both of the structured data around the South China Sea from traditional earth observation systems, such as remote sensing, hydro-meteorological, and natural resource data, and the unstructured data from the Internet, such as texts, pictures, and videos. Then, functions, such as information query, visualization, and analysis, are implemented. Integrations and inter-operations of the data and functions are mainly achieved by being published as a service. Finally, the system provides an effective way for the scientific management, analysis and decision making in the South China Sea.