An apparatus for dynamically controlling backlight source receives a pixel input data, and outputs a pixel output data and a PWM signal. The apparatus includes image analysis unit for receiving the pixel input data and outputting image data after performing image analysis. An information unit stores relation data including luminance adjusting data and PWM adjusting data corresponding to gray level range. A luminance calculation unit receives the image data from the image analysis unit and the relation data from the information unit, and calculates a required gray level corresponding to a required luminance, and outputs a required pixel luminance data and a required PWM data according to the required gray level. A PWM adjusting unit receives the required PWM data and outputs the PWM signal. A multiplication unit receives the pixel input data and performs luminance adjustment according to the required pixel luminance data for outputting the pixel output data.