Disclosed are a physical layer (PHY) protocol data unit (PPDU) transmission method and a related apparatus. The method includes: generating a PPDU, where the PPDU includes a universal signal field (U-SIG), and the U-SIG includes a subfield indicating that the PPDU is a null data packet (NDP); and sending the PPDU. In this way, a beamformee (Bfee) that receives the NDP can identify the NDP earlier. This helps improve efficiency of reading the NDP by the Bfee. The PPDU is an NDP used for a standard after 802.11ax. In a scenario in which wireless communication is performed by using the standard (for example, 802.11be) after 802.11ax, the Bfee can perform channel estimation based on the NDP.