The present disclosure provides an array substrate, a manufacturing method thereof, and a display device. The array substrate includes a base substrate, and a first functional layer and a second functional layer laminated one on another on the base substrate. The first functional layer forms a level-different region on the base substrate, and the second functional layer covers the level-different region. A portion of the first functional layer at the level-different region is provided with a target gradient angle, the target gradient angle is a maximum gradient angle when the second functional layer has a predetermined thickness, and the predetermined thickness is a thickness when a functional requirement of the second functional layer has been met and the second functional layer is not broken at the level-different region.