Abstract: With the development of internet technology, twitter, blog, forum and other virtual communities, more and more enterprises begin to borrow virtual communities to mobilize more network users for the participation in community's discussion and achieve the expansion of enterprise visibility. So for businesses, the most important is to mobilize virtual community user activity. This paper argues that the key of role identity theory is the individual's own understanding of the role and behavior, they are the role identity and role playing. The research results have practical value in enriching the role identity theory and enhancing user activity for the virtual communities.