The invention discloses a liquid crystal display device, which comprises a liquid crystal driver module, a backlight driver module, a liquid crystal panel and LED backlight, and is characterized in that the liquid crystal device also comprises an image signal receiver module, an image cache module, an image analysis module, a backlight brightness calculation module and a liquid crystal grayscale calculation module. The invention also discloses a processing method of the digital image signal. The invention adopts an entire screen backlight adjustment method with a liquid crystal grayscale compensation method to enable the backlight brightness to change according to the contents of the images, so that the power consumption can be reduced, the display contrast can be improved, and the effect of the display pictures can be ensured.