A method and an apparatus for transmitting an EHT PPDU in a WLAN system are proposed. Specifically, a transmitter generates an EHT PPDU and transmits, on the basis of an RF, the EHT PPDU to a receiver through a 320 MHz band in which an 80 MHz band is punctured. A legacy preamble includes an L-STF and an L-LTF. The legacy preamble is generated by applying a first phase rotation value. The first phase rotation value is determined on the basis of a first scheme and a second scheme. The first scheme is a scheme of obtaining an optimal PAPR in the L-STF and the L-LTF. The second scheme is a scheme of obtaining an optimal PAPR on the basis of the maximum transmission bandwidth supported by the RF. The first phase rotation value is obtained on the basis of a second phase rotation value and a third phase rotation value. The second phase rotation value is a phase rotation value that repeats a phase rotation value defined for the 80 MHz band in an 802.11ax system. The third phase rotation value is a phase rotation value defined in units of the 80 MHz band in the 320 MHz band.