Disclosed are a method and a device for transmitting and receiving data in a wireless LAN system. A connection method performed in a terminal comprises the steps of: transmitting a probe request frame; receiving, from a main-access point, a probe response frame which is a response to the probe request frame; and transmitting, to the main-access point, an ACK frame which is a response to the probe response frame if it is determined that an operation is performed in an uplink relay mode on the basis of information included in the probe response frame. Thus, the wireless transmission efficiency of a wireless LAN system is capable of being improved.