A thin film transistor and a manufacturing method thereof, an array substrate and a manufacturing method thereof, and a display device are provided. The thin film transistor is provided on a base substrate and includes: an active layer including a first surface and a second surface which are opposite to each other, in which the second surface is closer to the base substrate than the first surface; and a source-drain electrode layer including a source electrode and a drain electrode which are separated from each other and are respectively connected with the active layer; each of the first surface and the second surface is a non-flat surface, and the non-flat surface includes a plurality of depressions and a plurality of protrusions which are alternately arranged.