A power line method and system are provided. The power line transmission method is applicable to a power line network, where the power line network includes a main power line device configured to connect a cable network, and a plurality of slave power line devices configured to receive the power line network provided by the main power line device. The power line transmission method includes the steps of selecting an agent device from the slave power line devices located in a section where the power line network is broken and maintaining the power line network by connecting the slave power line devices located in the non-broken section of the power line network to the agent device through a wireless network function provided by the agent device.