The present disclosure proposes a method and a device for configuring a bandwidth field and an indicator bit to indicate a bandwidth of a TB A-PPDU in a wireless LAN system. Specifically, a reception STA receives a trigger frame from a transmission STA. The reception STA transmits a TB A-PPDU to the transmission STA via a 320 MHz band. The trigger frame includes a common information field, a special user information field, and a first and a second bit. The common information field includes a first bandwidth field. The special user information field includes a second bandwidth field. The TB A-PPDU includes an HE TB PPDU for a primary 160 MHz channel and an EHT TB PPDU for a secondary 160 MHz channel.