Abstract: Determination of the color display gamuts is the presupposition to convert color space in color management system.The triangular region produced by plotting the CIE1931 chromaticity coordinates of the red,green and blue display primaries and connecting them with straight line is often referred to as the color display gamut,which is not enough to describe generally the color display gamuts at all luminace.Because,the shape and size of color gamuts will change if the color luminance change.In this paper,the authors provide instruction on determining color display gamuts at all luminance.