As the related theory and technology of digital earth has been evolved since the concept of "digital earth" put forward by U.S. Vice President Al Gore, and more and more attention has been paid to ocean exploration and usage around the world in recent years, China ocean administration, together with oceanographers, proposes the "Digital Ocean" program from the state ocean development strategy point and puts it in the HI-TECH Research and Development Programs. "Digital Ocean", which comes from digital earth, has no exact definition currently and will be a large complicated project because it refers to many other technologies and methods such as wideband network, satellite remote sensing imagery data acquisition, mass data store and compression, interoperability, scientific computing, distributed objects, and virtual reality, spatial data warehouse, metadata database and Web GIS etc. China Digital Ocean Prototype System (CDOPS) which is the kernel part of “Digital Ocean”, is designed and constructed tentatively. It provides a visualization, presentation and spatial analysis platform for ocean three-dimensional monitoring data and information. Ocean administrations, professionals, military departments and common users will benefit from that system. In this paper, one kind of understanding of "Digital Ocean" in China is introduced firstly. And then the architecture of the CDPOS is put forward. In addition, the design and preliminary realization of the 9 sub-system functions are presented. At last, some key technology problems faced in constructing CDOPS are discussed.