Provided is a root mobile router and the operating method thereof in a dynamically composed moving network, capable of forming a self-configuring ad-hoc network between wireless personal area networks (WPANs) of each user in a moving network and supporting a stable connection between the network and the Internet. The method includes the steps of: receiving state information of multiple access networks and selecting an optimal access network in order to connect to the Internet; receiving a result of the selection and activating an interface of the selected access network; changing the selected access network to the activated access network interface; and updating routing path information automatically and stably transmitting an IP packet to the Internet through the selected access network interface. Therefore, a personal mobile terminal can be utilized as a mobile router.