The application provides an array substrate and a preparation method thereof, and a display panel, aiming at reducing the leak current of a thin film transistor of the array substrate and avoiding the problems that the display panel comprising the array substrate is not sufficiently charged and is low in picture retention rate. The preparation method of the array substrate comprises the steps of sequentially forming patterns of a gate electrode, a gate electrode insulating layer and an active layer on a substrate; then, forming patterns of photoresist layers, wherein the thickness of the photoresist layer at least in the first region is greater than the thicknesses of the photoresist layers in the other regions, and the orthographic projection of the first region on the substrate at least covers the orthographic projection of a channel region of the active layer on the substrate; removing the photoresist layers in the other regions except the photoresist layer in the first region; carbonizing the photoresist layer in the first region to form a pattern of a shading layer.