A method and system for increasing colour gamut of display device are provided, the method comprising following steps. Obtaining RBG value of image. Transferring RGB value from RGB space to HSV space for obtaining saturation of each solid color images of image. Determining whether if percentage of an area which saturation of each natural color is greater than first threshold value in solid color image is occupied on an area of whole image is greater than second threshold value. Adjusting RGB value of solid color image for obtaining adjusted RGB value of adjusted solid color image, if percentage of an area which saturation of natural color is greater than first threshold value in solid color image is occupied on an area of whole image is greater than second threshold value. Outputting adjusted RGB value of the adjusted solid color image.