An electric adjustment device for sofa headrest includes a first fixing member, a second fixing member, and a drive device having an output end that linearly reciprocates. One end of the second fixing member is pivotally connected to the first fixing member, and the drive device is pivotally connected to the first fixing member and arranged flush with the first fixing member. A sliding direction of the output end is perpendicular to a pivotal axis about which the second fixing member is pivotable to the first fixing member. Specifically, the second fixing member is extended downward to form a fixed end for fixing to a backrest support frame. The electric adjustment device is installed in the headrest support frame instead of the backrest support frame, so that other functional parts are installed inside internal space of the backrest support frame which improves the function of the sofa.