An OLED array substrate and a manufacturing method thereof, an array substrate and a display device are provided. The OLED array substrate includes a wire; a plurality of pixel units, each of which includes an OLED light-emitting unit, a driving transistor and a storage capacitor; an insulation layer which covers the driving transistor, the storage capacitor and the wire; and a conductive layer, which is on the insulation layer and is configured to provide a common voltage to the plurality of the pixel units. At least one of the wire, the driving transistor and the storage capacitor is overlapped with the conductive layer in a direction perpendicular to the OLED array substrate.