An array substrate and its manufacturing method, and a display device are disclosed, and the array substrate includes a black matrix (200) disposed on a base substrate (100) and has a plurality of pixel units arranged in an array, the orthographic projection of the pattern of the black matrix (200) on the base substrate at least partially covers the gap between adjacent pixel units, and the surface of at least a portion of the black matrix (200) has a first concave-convex structure (A) capable of reflecting the light irradiated to the surface of the black matrix (200) in diffuse reflection. Because the first concave-convex structure (A) of the surface of the black matrix (200) has a diffuse reflection effect, the external light will be subjected to diffuse reflection when irradiated to the surface of the black matrix (200), thereby reducing the light intensity of the reflected light, enhancing the visibility of the area of each of the pixel units of the array substrate, and improving the display effect of picture.