A power save mode-based operation method and device in a wireless LAN are disclosed. The power save mode-based operation method and device in a wireless LAN can comprise the steps of: transmitting, by an STA, a first trigger frame to an AP in a first service interval; receiving, by the STA, a downlink frame transmitted by the AP on the basis of the first trigger frame in the first service interval; receiving, by the STA, traffic indication information from the AP in a second service interval after reception of the downlink frame; determining, by the STA, whether a pending downlink frame of the AP exists on the basis of the traffic indication information in the second service interval; and determining, by the STA, a mode for saving power on the basis of whether the pending downlink frame exists.