Most traditional directory systems use tree structure. This structure has revealed some problems, especially in a large system domain like distributed networking environment. These problems are severe constraints on object naming, no support to automatic sharing, and single name space. We proposed a new directory structure called MSD (Multi-Space Directory) to solve these problems. MSD exhibits several outstanding characteristics over tree directory, such as supporting both hierarchical and orthogonal classifications, supporting both vertical and horizontal automatic sharings, providing multiple working environment, and providing a better mechanism for protection and consistency. This paper first analyzed the problems of tree directory and new requirements for directory systems, then describes the structure of MSD in detail and shows its merits over tree directory.