The invention discloses a HomePlug AV standard-based automatic relay networking method for a power line broadband carrier band. According to the method, each communication unit of a broadband carrier communication system is automatically enabled to be a relay node respectively, and any unit incapable of being in direct communication with a local terminal can automatically find an adjacent node. When a carrier node cannot register and get online with a master node, one carrier node is selected out of a routing list according to the current power grid environment and the signal condition. After that, the selected carrier node is adopted as a relay for realizing the communication with the master node without the need of manual intervention. When the carrier node successively registers at the master node via the above relay address, the node or the carrier master node can only be in communication with an opposite side only through the selected relay node. Therefore, the problem that the transmission distance is short in a power carrier communication system can be solved. Meanwhile, the data transmission reliability and the data transmission stability of the power carrier communication system are improved.