A plasma display device and driving method thereof has a peak value of one frame is detected and then converted. A grayscale or a grayscale value is converted according to an original peak value and a converted peak value, and a total number of sustain pulses applied to the one frame is reset such that a brightness corresponding to the converted grayscale or grayscale value is set to be equal to a brightness corresponding to the original grayscale or grayscale value. In such a manner, the numbers of on-subfields and useable subfields corresponding to the grayscale of the input video signal are increased, so that the discharge characteristics are enhanced and the false contour is reduced.