A method for transmitting an uplink frame in a wireless LAN system according to an embodiment of the present specification comprises the steps in which: a user STA configures a backoff counter for contention-based channel access according to first parameter information for multiple users when a first trigger frame for uplink transmission of the multiple users is received from an AP; the user STA performs a countdown operation on the basis of the backoff counter configured according to the first parameter information; the user STA interrupts the countdown operation in order to transmit a trigger-based uplink frame in response to a second trigger frame when the second trigger frame is received; and the user STA resumes the countdown operation, which has been interrupted, when an ACK frame corresponding to the trigger-based uplink frame is not received.