Abstract: This application relates to a method, an apparatus, and a system of power line communication (PLC) for the internet of things (IoT). The method includes: A sending device receives a first request from a receiving device, where the first request requests to perform channel assessment in a first time window in a power line communication periodicity; in response to the first request, the sending device sends a sounding signal required for performing channel assessment to the receiving device; the sending device receives a modulation parameter from the receiving device, where the modulation parameter is determined by performing channel assessment based on the sounding signal; and the sending device performs data transmission with the receiving device in the first time window based on the modulation parameter.