With the development of computer network and information, digital product is more and more popular. So the problem of protecting the digital product's copyright is urgent and important. Digital watermarking contains the copyright information and authentication information, and protects legal copy and distribution of digital products, which has been the hotspot of international academia. The paper analyze digital watermarking technology, and discuss its various algorithm, point out their characteristic and disadvantages. A good digital watermarking algorithm need to implement blind extraction, robustness and resistance of noise attacks, JPEG compress attacks, geometric attacks etc. In the end, the paper a introduce the current state of this technique and propose several directions of development of digital watermarking at next stage.