The cyberspace is a new context for the theoretical thinking of self and identity. Following the thinking of multiple identities suggested by Turkle, this paper argues that the multiple identities, as different sets of a role, may both provide self affirmation in our self system. This paper first tries to examine the interaction between the online-self and the offline-self. An online electrical survey for the board mangers in various BBS was conducted. With 349 responded questionnaires, we found that while the intensities of expressive ties and instrumental ties increase, the self-affirmation of the board managers is strengthened. Interestingly, when the online-self affirmation is strengthened, the offline-self affirmation is weakened.