In this application, a manner of generating a modulated field STF is enriched, so that a manner of generating a PPDU is enriched, thereby improving data transmission flexibility. The method includes: After generating a PPDU, a transmit end sends the PPDU to at least one receive end, where the PPDU includes at least one modulated field STF, the modulated field STF includes a plurality of zero elements and a plurality of non-zero elements, m1 zero elements are included before a first non-zero element, m2 zero elements are included after a last non-zero element, m1+m2 zero elements are included between any two adjacent non-zero elements, m1 and m2 both are positive integers, and the modulated field STF is mapped to a plurality of consecutive subcarriers for transmission. This application is used for data transmission.