The present invention discloses a method and an apparatus for controlling user's participation into a session so that the system can control accession to a PoC session requested by anonymous users and restrict an expelled user from joining the session again. Under the present invention, a client in the PoC session sends a request of expelling a user to the control server, with the SSRC identifier or nickname of the user or an anonymous user wildcard carried in the request; according to the received SSRC identifier, nickname or anonymous user wildcard, the control server searches for the corresponding PoC address, and expels the user out of the session as required according to the PoC address. Therefore, the client with the expulsion right can control accession to the PoC session requested by other users, especially anonymous users, thus keeping order of the session. The control server automatically rejects the reattempt of the expelled user according to the rejection list and the rejection policy, thus preventing such users from harassing the PoC session maliciously, and improving the service experience of the user.