The present invention discloses a liquid crystal display device and a control method thereof. In the present invention, a clock controller detects an external clock signal and outputs a switching signal according to the external clock signal. According the information carried by the switching signal, a shutoff switching circuit controls a gamma voltage generator and a common voltage circuit to output voltages making a pixel electrode and a common electrode have a zero voltage difference. Thereby, the pixel charges are completely released after system shutoff, and the shutoff retained images are instantly eliminated.