The present invention relates to a flat panel display device that is adaptive for preventing a brightness inversion phenomenon generated when the data modulated before are re-modulated in a multi-modulation method where data are modulated several times, and a data multi-modulation method thereof. The flat panel display device includes a first modulator which primarily modulates digital video data, which are to be displayed in a flat panel display panel, with pre-stored first compensation values in order to adjust at least any one of a response characteristic and a contrast ratio of the flat panel display panel. The flat panel display device further includes a second modulator which secondarily modulates the digital video data, which are to be displayed at a defect display area of which the brightness appears different from that of a normal display surface when displaying the same gray level in the flat panel display panel, with pre-stored second compensation values.