This paper reports a project named “General Rules of National Digital Library Metadata”, trying to build a metadata application framework for National Library of China (NLC). It aims at solving the applications of DC in Chinese digital library, developing a series of related standards, criteria and platform, to meet the requirements of describing, organizing, managing, serving and preserving the Chinese digital objects. It functions to support producing, processing, organizing, releasing, preserving and managing information resources in the digital library system of NLC, and then to achieve the interoperability and data sharing with other digital library systems to the more extent. The project outcomes are two parts: a metadata application framework and principles of National Digital Library of China based on the work of DCMI and the other international leading metadata projects, and a conversion program. According to this project, we are trying to find the best practice of metadata application for developing digital library in China.