Method and system for adding poc clients into poc group session composed of flexible target group

A method for adding PoC(Push to talk Over Cellular) group members to a PoC network and a system thereof are provided to enable a PoC user, participating in a group call, to transmit a single SIP(Session Initiation Protocol) REFER message through the present session in order to invite a preset specific PoC group and individual PoC users to the group call. A method for adding PoC(Push to talk Over Cellular) group members to a PoC network comprises the following steps of: transmitting a member addition request message for joining a random client and/or a random group to the current session; confirming whether a specific address is a group or not among object address information within the addition request message; transmitting a message for obtaining information about the random group to a group list server; and transmitting a session-participation message to a corresponding group by obtaining the group list information.