Now gamut mapping is usually implemented on two dimensional color planes, accordingly the gamut description is converted to the boundary description on hue profile. A method with least squares interpolation condition to fit the gamut boundary line piecewise was put forward through analysis of boundary shape and considering the accuracy and efficiency of gamut mapping. The result showed that the method can ensure the continuity of the gamut boundary; the fitting effect is close to that of piecewise linear interpolation method, which ensure the accuracy of gamut mapping; the greatest advantage of this method is the improvement of gamut mapping efficiency, which simplify gamut mapping.