An array substrate and a manufacturing method thereof are provided. The method for manufacturing the array substrate includes: forming a passivation layer on a base substrate; forming photoresist on the passivation layer, and forming a first photoresist pattern including a photoresist-completely-retained region, a photoresist-partially-retained region and a photoresist-completely-removed region, by exposure and development processes; forming a first through hole in the passivation layer by etching the passivation layer with the first photoresist pattern as a mask; forming a second photoresist pattern by performing ashing on the first photoresist pattern to remove the photoresist in the photoresist-partially-retained region and reduce a thickness of the photoresist in the photoresist-completely-retained region; and etching the passivation layer with the second photoresist pattern as a mask, so as to reduce a thickness of the passivation layer in the photoresist-partially-retained region.