The present invention discloses a method for realizing user identity association, the method comprising: setting an equivalent behavior user identifier in a Home Subscription Server (HSS); associating IMS Public User Identities (IMPUs) with the equivalent behavior through the set equivalent behavior user identifier. The present invention also discloses a system and a device realizing user identity association. According to the embodiments of the present invention, the association of the IMPUs with the set equivalent behavior is realized, which improves the user experiences.