The invention discloses an electric stay bar for automatically opening and closing a tail door of a sedan. The electric stay bar comprises a housing, wherein the housing comprises a first housing anda second housing, which are hollow and communicates with each other through a first cavity; a tension spring is arranged outside the second housing in a sleeving manner; a motor is coaxially mounted in the first housing and drives a driving wheel in the first housing to rotate; a driven wheel is mounted in one end of the second housing; a driven wheel fixing shaft of which one end is connected toone end of a lead screw through a lead screw shaft sleeve is arranged in the driven wheel in a sleeved manner; the end, away from a nut, of the lead screw is fixed at one end of the second housing adjacent to the lead screw; and the driving wheel drives the driven wheel to rotate through an intermediate gear. The electric stay bar is small in arrangement space, short and suitable for the sedan andcan effectively prevent the motor from damage caused by blocked rotation.