A display data adjustment method is provided, including the following. First display data is received, and first grayscale values of first sub-pixels of different colors in the first display data are converted from a first color gamut space into color values in a second color gamut space. First weight values are generated according to the color values. Lookup tables are compared according to the first grayscale values of the first sub-pixels to obtain groups of first high grayscale values and first low grayscale values corresponding to the first sub-pixels. Second high grayscale values and second low grayscale values are obtained by calculation according to the groups of the first high grayscale values and the first low grayscale values and the first weight values. The second high grayscale values or the second low grayscale values are selected as second grayscale values of second sub-pixels in second display data.