The invention discloses a high-gamut light diffuser which comprises 70-99 parts of raw material and 1-30 parts of optical master-batch .The optical master-batch is a mixture of red optical master-batch and green optical master-batch, and the additive amount of the red optical master-batch and the additive amount of the green optical master-batch each account for 1-15 parts .The light diffuser is an improvement in a light diffuser applied to a straight downward display screen backlight source and is prepared through the following method, the gamut value of the light diffuser can be remarkably increased, and the color rendition degree of a display screen can be greatly increased .One or a mixture of more of light-transmitting PP plastic particles, PC plastic particles, PMMA plastic particles, ABS plastic particles, PS plastic particles and MS plastic particles is used as the raw material; the raw material, a lubrication dispersing agent and red phosphors are taken according to proportional parts by weight and pelleted into the red optical master-batch; the raw material, a lubrication dispersing agent and green phosphors are taken according to proportional parts by weight and pelleted into the green optical master-batch; lastly, the raw material, the red optical master-batch and the green optical master-batch are mixed to be uniform according to proportional parts by weight and then charged into a double-screw extruder, and diffuser sheets are formed.