A COA substrate is provided including a substrate base, a first metal layer, a first insulating layer, a semiconductor layer, a second metal layer, a color resist layer, and a pixel electrode layer. The surface of the color resist layer is provided with a protrusion and a recess, and the pixel electrode is disposed on the protrusion and the recess. A plurality of protrusions and a plurality of recesses are provided, thereby increasing the display quality of a liquid crystal display device.