A thin film transistor and a fabrication method thereof, an array substrate, and a display panel are provided. The fabrication method of the thin film transistor includes: forming an active layer on a base substrate, the active layer including a channel region; forming an amorphous carbon layer on a region of the active layer other than the channel region; and forming a source electrode and a drain electrode on the amorphous carbon layer, the source electrode and the drain electrode being respectively electrically connected with the active layer through the amorphous carbon layer.