The present invention relates to a wireless communication system, and more specifically, disclosed are a method and an apparatus for accessing a channel in a WLAN system. A method for synchronizing channels from a station (STA) in the wireless communication system, according to one embodiment of the present invention, comprises the steps of: receiving from an access point (AP) setting information with respect to an least one slot allowing channel access by the STA; receiving a synchronization frame from the AP from a slot boundary of the at least one slot; and synchronizing the channels on the basis of the synchronization frame, wherein the synchronization frame may be a null data packet (NDP) frame.