A method of obtaining luminance and chromaticity of white in the RGBW display using RGB display, including; obtaining spectral values of a q grayscale of red sub-pixels, green sub-pixels and blue sub-pixels of the RGB display; obtaining spectral values of red, green and blue sub-pixels of a color filter in the RGB display; calculating a spectral value of the q greyscale of white in the RGB display as a spectral value of the q grayscale of the white sub-pixels of the RGBW display; calculating tristimulus values WXq, WYq and WZq of the q greyscale of the white sub-pixels of the RGBW display; using the stimulus value WYq as a luminance of the q greyscale of the white sub-pixels of the RGBW display, and using the formulae x = WX q WX q + WY q + WZ q ⁢ ⁢ and y = WY q WX q + WY q + WZ q to calculate a chromaticity (x, y) of the white sub-pixel of the RGBW display.