Disclosed herein relates to a sleep mode operation method, and the sleep mode operation method according to the present invention may include transmitting a sleep request message for requesting sleep mode switching to a base station; receiving a sleep operating parameter including a sleep cycle and a listening window from the base station; referring to the sleep operating parameter to switch to a sleep mode; receiving a traffic indication message indicating that traffic is generated from the base station; receiving traffic from the base station during the listening window while at the same time operating a timer; and early terminating the listening window to enter into a sleep window if the timer operation is expired according to the traffic reception prior to terminating the listening window.