Embodiments of the present invention relate to an array substrate, a manufacturing method thereof and a display device. The manufacturing method of the array substrate comprises: preparing a base substrate; forming a gate electrode pattern on the base substrate; forming a gate insulating layer pattern on the base substrate with the gate electrode pattern formed thereon; and forming an active layer pattern, a pixel electrode pattern and source and drain patterns above the gate insulating layer pattern through a three-gray-tone mask process in one patterning process, wherein the gate electrode pattern, the active layer pattern, the source pattern and the drain pattern constitute a thin film transistor.