On the basis of analyzing the characteristics of content components in the current distance education technology specifications, this paper puts forward an Open Content Object model for the Web-based learning content by extending the Sharable Content Object (SCO) of the Sharable Content Object Reference Model (SCORM) which was established by the Advanced Distributed Learning (ADL) of the Office of the Secretary of Defense (OSD). In this components model, the Open Content Object has the function of requesting services and providing services by the messages passing mechanism which takes the Learning Management System (LMS) as scheduling center of messages, thus the content components can not only be aggregated to compose higher-level units of instruction, but also can form the interoperable associational relationship, thereby it can provide a more flexible and effective approach to the design of the interoperable aggregation and sequence of the Web-based learning content. (Contains 6 figures.)