Provided is an association control method for maximizing a message in message (MIM) function in a WLAN environment. According to an exemplary embodiment of the present invention, when all SINR values of transmission links to two or more first clients associated with the first access point are equal to or more than a predetermined capture threshold, SINR value of a transmission link to a second client associated with the second access point is less than the capture threshold, and at least one of the first clients, referred to as a third client group, can be associated with the second access point, associations are modified so that the third client group is associated with the second access point to enable concurrent transmission.