In order to improve the reliability and the coverage of power line communication (PLC) and satisfy the communication demands of smart distribution grids, this paper proposes a novel cross-band cognitive PLC (CC-PLC) method, where the cross-band incorporates low-frequency band, medium-frequency band and high-frequency band concurrently. The core concept is to enable PLC node to choose its working frequency and communication bandwidth within the cross-band frequencies according to its local channel conditions. By using this paradigm, the communication parameters of PLC can be adjusted on-line, and the disadvantages of traditional narrow-band and broadband PLC, where the working frequencies are preset and can not adapt to the specific and varying channel characteristics, can be well overcome. Moreover, this paper presents some promising key technologies, including channel sensing based on preamble sequence, on-line self-defined physical layer based on equivalent complex base-band (ECB), and self organized network based on multi-frequency flooding. All these solutions have remarkably improved the PLC’s frequency utilization efficiency and its network coverage. A CC-PLC system based on 150 kHz12 MHz is independently developed for field test, which validates the superiority of CC-PLC and reveals its favorable practical prospect in the smart grid.