The present invention provides a CIE Lab color space based color conversion method, which includes converting two-dimensional color planes Ln and Ln-1 of original diagram data into two-dimensional color planes Ln′ and Ln-1′; according to a plane Lx of any lightness level between the known Ln and Ln-1, calculating Lx′ between Ln′ and Ln-1′ and having the same lightness level as Lx; calculating a conversion matrix between Lx and Lx′; calculating color-converted and adjusted target color according to the color of any one point of the original diagram data; and completing color space of the target color. The present invention also provides a CIE Lab color space based color conversion device and a liquid crystal display device. With the above method, the present invention allows of easy construction of reverse conversion model. The algorithm can be easily implemented and the operation speed is increased.