This application provides a method and apparatus for transmitting a physical layer protocol data unit, so as to design a long training field sequence for a larger channel bandwidth. The method includes: generating a physical layer protocol data unit PPDU, where the PPDU includes a long training field, a length of a frequency domain sequence of the long training field is greater than a first length, and the first length is a length of a frequency domain sequence of a long training field of a PPDU transmitted over a channel whose bandwidth is 160 MHz; and sending the PPDU over a target channel, where a bandwidth of the target channel is greater than 160 MHz.