Embodiments of the present invention provide a thin film transistor and a manufacturing method thereof, an array substrate including the thin film transistor, and a manufacturing method of the array substrate. The thin film transistor comprises an active layer, a gate insulation layer, a gate, an interlayer insulation layer, a source and a drain formed on a base substrate, the interlayer insulation layer and the gate insulation layer are provided therein with through holes corresponding to the source and the drain; the active layer comprises a source ohmic contact region connected with the source, a drain ohmic contact region connected with the drain, a channel region serving as a channel located below the gate, and a lightly doped region between the drain ohmic contact region and the channel region.