The present invention relates to a wireless communication system, and more particularly, to a method and an apparatus for accessing a channel in a wireless LAN system. According to one embodiment of the present invention, a method for performing channel access by a station (STA) of a wireless communication system comprises: a step of receiving, from an access point (AP), information about the time window which does not allow channel access of a traffic indication map (TIM) mode STA; and a step of performing channel access based on the time window. In the event that the STA is a non-TIM mode STA, the channel access is performed in the time window. In the event that the STA is a TIM mode STA, the channel access is performed in the time interval indicated by the TIM, excluding the time window.