A thin film transistor, an array substrate and manufacturing method thereof, and a display device are provided. The thin film transistor includes an active layer, a source electrode, a drain electrode, and a first gate electrode, the first gate electrode is shaped in a ring. The active layer includes a first portion, a second portion and a third portion for connecting the first portion and the second portion. The first portion and the second portion are disposed horizontally, and connected to the source electrode and the drain electrode, respectively. The third portion is disposed obliquely, and has a channel provided thereon. At least one part of the channel is located on an inner side of the first gate electrode. The thin film transistor can be used in a display device.