The invention provides a luminance adjustment method and apparatus for RGBW LCD, which uses first and second EOTFs to generate a grayscale luminance lookup table for RGBW LCD, and makes the grayscale-luminance relation in lookup table corresponding to the first EOTF within the grayscale interval between 0 and grayscale threshold; the grayscale-luminance relation in lookup table corresponding to the second EOTF within the grayscale interval between grayscale threshold and 255; the curve slope of the second EOTF greater than the curve slope of the first EOTF within the interval between second luminance threshold and maximum luminance value. By adopting different EOTFs for low and high grayscale intervals, the method considers the poor dark state characteristics of LCD and characteristics of RGBW LCD having higher maximum luminance, and improves the display capability of RGBW LCD in details of high grayscale images.