A thin film transistor and a manufacturing method thereof, an array substrate and a display device are provided. The thin film transistor is formed on a substrate and includes: an active layer on the substrate, the active layer including a source region, a drain region, and a channel region between the source region and the drain region; a first gate electrode on a side of the active layer away from the substrate; and a second gate electrode on a side of the first gate electrode away from the substrate, wherein a thickness of the first gate electrode is smaller than a thickness of the second gate electrode.