The invention discloses a dynamic control method of edge light LED (Light Emitting Diode) backlight used for liquid crystal screens. The edge light LED backlight comprises a plurality of groups of LEDs. The method comprises the following steps of: obtaining grayscale data of an original image of a current frame in video signals; obtaining first optimization brightness data of each group of LEDs according to the grayscale data of the original image of the current frame and data of a contribution rate of each group of LEDs to backlight; performing histogram statistics of the number of grayscale pixels to the grayscale data of the original image of the current frame, and determining a whole threshold grayscale according to the result of the histogram statistics; obtaining second optimization brightness data of each group of LEDs according to the first optimization brightness data of each group of LEDs and the whole threshold grayscale; and regulating the data of the original image of the current frame according to the second optimization brightness data of each group of LEDs, and generating output image data of the current frame. According to the method, the visual effect of a screen is guaranteed. Additionally, the power consumption of the backlight is greatly reduced, and the contrast of the screen is increased.