In Liquid Crystal Display (LCD) backlight local dimming technology, to ensure the resulting image quality and luminance, accurate pixel compensation is necessary after each region backlight level been determined. Low pass filter was used to simulate the process of Light-emitting Diode (LED) backlight diffusion to get the LED light spread function and the actual backlight level of each pixel, and then according it to compensate the pixel. On the direct-backlight LCD,specific images were used to verify the accuracy of the method. This method with common test platform has a high precision and a simple system. The experimental validation results show that the average relative error is 6.41% when the number of the direct-backlight region is 32. The diffusion method was used in the dynamic local dimming LCD TV. The energy-saving rate reaches 27.06%, and the screen appears no tailing phenomena.