Based on discussion on general methods of constructing global directory in DSMDS (Distributed Spatial Database Management System), a new approach based on relation model was brought forward. It specifies three main components of the global directory, including directory organization, directory update and extern interface. Then the authors implemented an actual global directory named SDirectoryService as well, key approaches and techniques in implementation were discussed in detail. Some experiments were designed and performed to check the efficiency, correctness and feasibility of the global directory, which reveal the directory works well on each aspect. By using the directory effective global query processing was achieved in DSMDS.