The present invention relates to a frequency-based online auto-defined multi-frequency power line carrier communication network, comprising one or more of a broadband node, a narrowband node and a cross-band nodes; the nodes using flexible digital front-end technology to accomplish, by means of frequency cognition, online frequency definition to constitute a multi-frequency communication network; the multi-frequency communication network uses a plurality of different operating frequencies for communication, the frequencies used for different runouts between two end-to-end nodes may be different from each other, and uplink and downlink frequencies on the same link may be different; the multi-frequency communication network supports communication between a broadband node and a narrowband node. In the technical solution of the present application, the flexible digital front-end technology is extended from a point-to-point system to a power line carrier communication network to withstand changes of power line carrier channels due to actual conditions, thereby improving the reliability and stability of the power line carrier communication network.