Semantic Web provides us with a new paradigm of Web based knowledge sharing and management. In this paper, an open knowledge service architecture (OKSA) is described, which emphasizes how to organize, discover, utilize, and manage web knowledge resources. Three kinds of knowledge service (KS) are identified, they are: OntoKS for retrieving, browsing and managing Web ontologies, RuleKS for facilitating the building of rule-based expert system and CaseKS for case-based experience knowledge management. These KSes provides value-added Web services from distributed Web knowledge resources. We use an application scenario from the traditional Chinese medicine area to clarify the design rationale of the KS model.