A thin film transistor (TFT) array substrate includes a substrate, a plurality of scan lines, a plurality of data lines, a plurality of thin film transistors, a plurality of pixel electrodes, and a plurality of pairs of repair pads is provided. A plurality of pixel regions are defined by the scan lines and the data lines over the substrate. The thin film transistors are disposed in the pixel regions and driven by the scan lines and the data lines. Each pixel electrode is disposed in the region, and is electrically connected to the thin film transistor. The repair pads are disposed under the data line. In addition, the repairing process includes welding the defective data line with the quasi-welding repair pad, and then forming a repair line to reconnect the defective data line.