The invention provides an array substrate, a manufacturing method of the array substrate and a display device. The array substrate includes a substrate base, and a grid line and a data line which are arranged on the substrate base; multiple pixel regions are defined by the grid line and the data line and are each internally provided with a diffuse reflection layer, and the surface, toward the light-out side of the array substrate, of the diffuse reflection layer is uneven. According to the array substrate, the diffuse reflection layer arranged in the pixel region of the array substrate can conduct diffuse reflection on external light, so that the brightness of the display device with the array substrate in an outdoor environment is improved, and the display effect in the outdoor environment is improved. In addition, since the brightness of the display device is improved through the external light, the energy consumption of the display device is not increased.