Example methods and devices for sending a beam refinement protocol packet are provided in this application, which support a transmission format of multi-channel transmission and multi-antenna transmission. One example method for sending a beam refinement protocol packet includes determining a transmission format of a beam training (TRN) subfield by a first device based on first information. The first information includes information indicating a quantity of transmit chains used for transmitting the TRN subfield on each channel and information indicating a channel aggregation mode. The first device sends a beam refinement protocol packet to a second device on a transmit chain based on the transmission format, where the beam refinement protocol packet includes a data field and a TRN field, and the TRN field includes a plurality of TRN subfields.