A method and a system for improving saturation degree of a RGBW image are provided. The method comprises: a step A of dividing a screen into a plurality of screen sub-regions according to a region range in which backlight is independently and dynamically adjustable; a step B of dividing the RGBW image to be displayed into sub-areas on the basis of the screen sub-regions, the sub-areas of the RGBW image to be displayed corresponding to the screen sub-regions; a step C of determining the sub-areas having saturation degree to be adjusted in each sub-area of the RGBW image to be displayed; and a step D of reducing backlight brightness of the sub-areas having saturation degree to be adjusted by a predetermined proportion when the RGBW image to be displayed is displayed. By means of the method and the system, saturation degree of the RGBW image may be adjusted finely.