Abstract: The main constraint in message transmission is security. The key must be shared among users so that we have a secure transmission in group based message transmission. In this paper we discuss an important security problem that happens in mobile ad hoc network for key agreement in dynamic group. For a communication to be secure, a group key must be shared by all the members of the group. The key must be updated when any member of the group leaves existing group or become a new member of the existing group. In this paper, we establish a secured transmission. The main idea here is to spilt the existing network into smaller sub-network and each sub-network maintains its own keys. These keys should be updated when a existing node leave the network or when an new node joins the existing system. The nodes that have the high stability in the sub-network will be made as the Inner gateway member and among Inner gateway member the one that has high stability will be made as Outer gateway member.