Automatic annotation can help to improve tagging or indexing of contents. If annotated properly, with a well organized thesaurus, a featured term map can be extracted from each text. With these featured maps, contents of these texts can be identified from each other, links to terms can be extended to other vocabularies, even in other languages, that make possible to automatic key work tagging, and ease the job of search engine. A network analysis method can make automatic annotation more accurate. And the thesaurus can also get benefits from annotation results to improve its structure.