A system for driving a liquid crystal display is provided. The system receives a video signal including a first predetermined gray level signal and a second predetermined gray level signal. The system includes a memory, an impulse signal module, a first multiplexer and a detection unit. The memory stores the first predetermined gray level signal. The impulse signal module receives the first and second predetermined gray level signal to generate a plurality of impulse signals. The first multiplexer receives the plurality of impulse signals and outputs the second predetermined gray level signal or the plurality of impulse signals according to the first control signal. The detection unit generates a first control signal to be applied to the first multiplexer according to the first predetermined gray level signal and the second predetermined gray level signal.