With the development of digital campus in university, more and more application systems have been used. In these systems, authentication function has been repeatedly design, which can be easy to cause multiple accounts and passwords, and brought inconvenience to users and administrators. Unified identity authentication system based on LDAP is a good solution to this problem. In this paper, based on the analysis of LDAP protocol and CAS, the unified identity authentication system built for digital campus is designed and implemented, and LDAP management system is also developed to achieve unified management of directory information in the university.