A pixel structure and its driving method, which are used in the active matrix organic illuminated displays, are described. The pixel structure has four transistors, a capacitor and three signal lines. The first and second transistors are used as the switching transistors and controlled by the first and second scan lines, respectively. The third and fourth transistors together constitute a current mirror to equalize the current flows through the OLED in each pixel and the writing in current in the data line. Therefore, the illumination of the OLED between each pixel will be more uniform and is not influenced by the threshold voltage.