A method for performing an uplink (UL) multi-user (MU) transmission performed by a station (STA) device in a Wireless LAN (WLAN) system according to an embodiment of the present invention may include receiving a Downlink (DL) MU Physical Protocol Data Unit (PPDU) including a physical preamble and a data field; and where the data field includes at least one Mac Protocol Data Unit (MPDU), where the at least one MPDU includes a trigger frame or a MAC header, where the trigger frame or the MAC header includes trigger information for a UL MU transmission of an ACK (Acknowledge) frame, and performing a UL MU transmission of the ACK frame in response to the DL MU PPDU based on the trigger information.