A method for performing channel access in an unlicensed band by a base station in a wireless communication system according to an embodiment of the present invention may comprise the steps of: sensing, in an unlicensed band, a carrier for transmitting a downlink signal; and transmitting the downlink signal when power detected by sensing the carrier is less than an energy detection threshold set by the base station, wherein the energy detection threshold is set to be equal to or less than a maximum energy detection threshold determined by the base station, and when another radio access technology (RAT) sharing the carrier exists, the maximum energy detection threshold is adaptively determined depending on the bandwidth size of the carrier, using the value, in decibels, of the ration between a reference bandwidth and the bandwidth of the carrier.