A method for driving a normal black type liquid crystal display (LCD) includes driving the LCD by applying uncompensated source signals corresponding to gray levels; recording first optimized common signal voltages (Vcom-opt1) of common signals corresponding with the gray levels; adjusting the source signal to drive the LCD so second optimized common signal voltages (Vcom-opt2) of common signals corresponding with the gray levels conform to the following conditions: (1) when the gray level is lower than a predetermined gray level, the Vcom-opt2 exceeds a predetermined voltage of the common signal and the absolute difference between the Vcom-opt2 and the predetermined voltage is less than or equal to that between the Vcom-opt1 and the predetermined voltage; and (2) when the gray level exceeds the predetermined gray level, the absolute difference between the Vcom-opt2 and the predetermined voltage is less than or equal to that between the Vcom-opt1 and the predetermined voltage.