The present invention relates to synchronizing a terminal and a server in a shadow area of service in a push-to-talk (PTT) service system. An alive report packet is periodically transmitted to a server by a terminal having no permission to send a talk burst. A talk burst idle packet is periodically transmitted to each session-established terminal by the server in an idle state. Sessions are ended between each terminal and server if either the alive report packet or the talk burst idle packet are not received for a certain time. Accordingly, synchronization between the server and the terminal is periodically certified, unnecessary traffic generated due to inconsistent synchronization is decreased, and quality of service is enhanced.