Provided is a manufacturing method for an array substrate, which relates to the technical field of displaying and comprises the steps of: S1: forming a pattern which comprises a first gate electrode (2) on a substrate (1); S2: forming a second gate electrode (4) above the first gate electrode (2) on the substrate (1) after step S1, and conducting oxidation treatment on the surface of the second gate electrode (4) to form a gate-insulating layer, the first gate electrode (2) and the second gate electrode (4) forming a gate electrode together; and S3: forming a layer-level structure of a pattern which comprises an active layer, source and drain electrodes, a data line, a passivation layer and a pixel electrode on the substrate after step S2. Also provided are an array substrate and a display device.