A dynamic backlight adjustment method for a display screen is provided. The method includes a step of dividing a display screen into multiple sub-areas, and executing following steps to one sub-area of the multiple sub-areas: (a) determining a maximum grayscale value of video input signals of the one sub-area when a current frame image is displayed, (b) determining a backlight brightness corresponding to the maximum grayscale value according to a relationship between multiple preset grayscale intervals and multiple backlight brightnesses and (c) adjusting a backlight brightness corresponding to the one sub-area to the backlight brightness corresponding to the maximum grayscale value. Using the dynamic backlight adjustment method, the smoothness in the dynamic backlight adjustment process is better, and the transition of bright and dark of the display screen is more nature.