A method for a WLAN system of the present invention comprises receiving, by an AP, a request frame requesting change of operating mode of a receiving STA associated with the AP from the receiving STA, wherein the request frame includes a control indicator indicating whether the receiving STA participates in UL MU MIMO transmission, and transmitting a trigger frame for a plurality of user STAs participating in the UL MU MIMO transmission based on the request frame, wherein the trigger frame includes identification information for the plurality of user STAs, resource allocation information for allocation of uplink frequency resources allocated individually for the plurality of user STAs, time information indicating a time interval during which the UL MU MIMO transmission is performed, and coding information indicating a channel coding scheme allocated for each of the plurality of user STAs.