Abstract: A thin film transistor (TFT) array panel structure and a fabrication method thereof are provided. The method includes the following steps. An insulating substrate is provided, on which a first metal layer is deposited to form a plurality of gate electrodes, a plurality of lower electrodes of storage capacitors, a plurality of scan lines, and a plurality of scan line pads with a first mask process. A TFT island region is formed with a second mask process. Drain electrodes and source electrodes of the TFT, upper electrodes of storage capacitors, pixel electrodes, data lines and data line pads are formed, and a plurality of pixel display regions is defined with a third mask process. The pattern of a passivation layer is defined with a fourth mask. A second metal layer in the pixel display region is removed by selective etching.