OPAC system is mainly for users (not staff), and its function is relatively simple, mainly for querying library documents, and now it also begins to include some personalized service functions for users;

The library management system is a professional work system for library staff (password login is usually required), which provides professional management functions such as interview, cataloging and periodical management.

If you still want to know, from the perspective of software development, because OPAC is user-oriented, it basically adopts easy-to-use B/S structure, while the management system still adopts C/S structure for security and stability.