In recent years, with the development of Digital Library and network technology, the reproduction of digital Resources of books and materials, such as the use of communication network, has become more and more popular. The copyright protection of digital library has also been paid more and more attention by the academic circle. In this paper, a robust watermarking technique based on DCT transformation is introduced to illustrate the application of digital watermarking technology in copyright protection of library digital resources. The experimental results show that using digital watermarking technology can protect copyright and information security and solve the copyright protection problem of digital library.