A level regulation circuit of a common signal of an LCD generates a first level voltage and a second level voltage according to a common voltage so as to generate a first common signal and a second common signal. Each pixel of the LCD includes two storage capacitors receiving the first common signal and the second common signal respectively. The level regulation circuit of the common signal uses an operational amplifier and one or two Zener diodes to generate the first level voltage and the second level voltage. The first level voltage and the second level voltage have the same voltage difference to the common voltage, so the flicker of the LCD can be reduced.