A thin film transistor array substrate and its manufacturing method are disclosed. A thin film transistor (TFT) includes a gate electrode formed on a substrate, and source and drain electrodes formed on the gate electrode and separated from each other. A common line made of the same material as the gate electrode is formed on the substrate. A storage capacitor includes a storage electrode connected with a storage electrode line and a pixel electrode formed on the storage electrode. The storage electrode and the pixel electrode are formed by patterning a transparent conductive film, and accordingly, light can be transmitted through the region where the storage capacitor is formed to thus increase an aperture ratio.