The present invention discloses a method for RGB color space gamut conversion, including: projecting any point o in RGB color space having source graphic data onto points N, M, mapped to coordination points in source cube; projecting point o′ corresponding to point o onto points N′, M′, mapped to coordination points in target cube; based on coordination points in target cube, computing points N′, M′; based on points N′ and M′, computing point o′ in target cube corresponding to point o in RGB color space having source graphic data; and computing target color after color conversion from any point in source graphic data. The invention also discloses an apparatus for RGB color space gamut conversion and an LCD device. With this, it is possible to perform color conversion in RGB color space, adjust color performance of output in hue and color purity, and accentuate specific colors.