This paper describes the concepts and the model of a digital library (UL)as well as overview of DL in the world. A real digital library model shouldconsist of four structure levels which are user interface) networks and communications, information resources and reference service system. There arefive functions in the DL which are digitized documents for various media, largestores, quick access fast transfers, privilege and management. We are creatingthe prototype of the digital library in Shanghai Jiao Tong University. They include a goal and content built SJTU DL, an environment of hardware and software and digital library support services and agents.