Tag, a kind of social annotation, is an essential component of online social networks and Web2.0 application. Research on it can reveal some patterns of userspsila activities on the Internet. This paper uses data from the social bookmarking site del.icio.us to examine the tagspsila network as a social network. We connected tags with common bookmarks to form a graph of tagspsila network and study it with the methods of complex network. After analysis, we found this network has the properties of small world and scale-free. We believe this result is useful for both research and system design.