Metadata is the information that describes the most important feature of an object. In recent years, metadata plays a more and more important role in data intensive applications. In this paper, we propose a semantic metadata catalog service, Semantic MCS. Semantic MCS has a well-organized data management model and supports the query mechanism using Ontology inference. Furthermore, we discuss the main problems that we met in real Grid applications. We propose a framework of metadata interoperation to resolve the problem of the services interoperability. And we propose a dynamic framework for metadata management for the rapid changing metadata in Grid.