A dynamic global backlight dimming algorithm is proposed based on the analysis of the Cumulative Distribution Function (CDF) of 12 local images histogram. For each image, the proposed algorithm decided Backlight Luminance (BL) dynamically from maximum CDF luminance ratio of 12 local regions instead of the value of the whole image. Ratios of backlight luminance are defined between 0.6 and 0.9, in order to preserve quality of images and decrease power consumption. The experimental results show that the improved method significantly improves the image quality of Liquid Crystal Display (LCD) and substantially reduces the power consumption, which also meets requirement of the PSNR rule.