A system and a method for controlling a power line network are provided. In the system and the method, a control unit device in every control network generates its own control network identification (CNID) and sends query messages to the other control networks to ensure each CNID is unique in the signal-reachable networks. The system and the method differentiate messages of the local control network from messages of the other control networks based on received signal strength of the messages in order to correctly demarcate multiple control networks.