The present invention provides a liquid crystal display, comprising a first circuit board and a second circuit board and a source driving circuit which are electrically coupled to the first circuit board, wherein the first circuit board comprises a sequence controller, and the sequence controller provides a control signal and codes the control signal, and transmits the coded control signal from the first circuit board to the source driving circuit through the second circuit board, and the sequence controller directly outputs the uncoded control signal through the first circuit board to ensure a phase delay relationship between the uncoded control signal and a control signal outputted by the source driving circuit. The present invention further provides a control signal debugging method applied with the aforesaid liquid crystal display.