The present disclosure provides an array substrate, a manufacturing method thereof and a display device. The array substrate includes an active layer, a gate insulating layer and a gate electrode layer formed sequentially on a base substrate. The active layer includes a first heavily-doped region, a first lightly-doped region, a first non-doped region, a second lightly-doped region, a second non-doped region, a third lightly-doped region and a second heavily-doped region which are sequentially arranged in a horizontal direction.