A drive method used for a plane monitor and a related drive device thereof are disclosed. The drive method comprises receiving image data corresponding to a picture, wherein the grayscale of the picture is between a first grayscale and a second grayscale; generating plural frame signals corresponding to the plane monitor; dividing each frame signal into plural sub frame signals, and dividing the plural sub frame signals of each frame signal into a first sub frame signal group and a second sub frame signal group; according to first grayscale and the second grayscale adjusting the level of the plural sub frame signals of each frame signal so as to make the grayscale displayed by the pixel corresponding to each frame signal equal to the grayscale of the picture; wherein under the condition that the number of the plural sub frame signals of each frame signal is X+Y, the number of the sub frame signals, corresponding to the N+1 grayscale, of the first sub frame signal group is X, and the number of the sub frame signals, corresponding to the N grayscale, of the second sub frame signal group is Y, the N+(X/(X+Y) grayscale displayed by the pixel corresponding to each frame signal can be interpolated.