A method for a station (STA) not having an association identifier (AID) allocated thereto transmitting a signal in a wireless LAN system, according to one embodiment of the present invention, comprises the steps of: transmitting a first frame through at least one resource among resources indicated by a trigger frame; and receiving a multi-STA block Ack (M-BA) frame as a reply to the first frame, wherein, if in the M-BA frame a MAC address of the STA that is different from a first information is detected from at least a part of a first field reserved for the first information, an N-bit of a second field preceding the first field is set as a temporary AID of the STA.