The present invention provides a method for manufacturing an array substrate, an array substrate, and a display device. The method for manufacturing an array substrate comprises: forming a pattern comprising a pixel electrode and a pattern comprising a gate of a thin film transistor on a substrate; forming a gate insulating layer; forming a pattern comprising an active layer and a source and a drain, which are provided on the active layer, of the thin film transistor by a patterning process; forming a passivation layer; forming a pattern comprising a main via penetrating through the gate insulating layer and the passivation layer and a main-via extension portion under a portion of the drain by a patterning process, wherein the main via is connected to the main-via extension portion; removing a portion of the drain which protrudes above the main-via extension portion so as to form a pattern comprising a final via; and forming a pattern comprising a connection electrode and a common electrode, wherein the connection electrode electrically connects the drain to the pixel electrode through the final via.