The invention discloses an array substrate and a preparation method thereof, and a display panel, so that a problem that the brightness of a TFT-LCD is affected because of backlight transmittance reduction due to a pixel electrode and common electrode that are formed by a semi-transparent metal film layer parallel to a substrate in the array substrate that is prepared by the existing technology can be solved. The array substrate comprises a substrate unit and a plurality of pixel units arranged on the upper surface of the substrate unit; and the pixel units are distributed on the substrate unit in an array mode. A first electrode groove and a second electrode groove are formed in the substrate unit, wherein the first electrode groove and the second electrode groove correspond to each pixel unit and extend from the upper surface to the lower surface of the substrate unit. Besides, the pixel units contain pixel electrodes and common electrodes; the pixel electrodes are formed in the first electrode groove; and the common electrodes are formed in the second electrode groove.