Considering LED as the extended source, a design method based on irradiance-segmentation-feedback was proposed to design very compact optical freeform surface for LED, then a high distance-height-ratio (DHR) direct-type backlight can be realized. Corresponding to the generation of optical sub-surfaces in optical surface construction, the total irradiance was segmented into sub-irradiances. After all sub-irradiances were adjusted by modifying optical sub-surfaces, the total irradiance was similar enough to the goal irradiance, meanwhile the desired optical surface was obtained. This design process needs no simulation and it is easy to operate and widely applicable. As an example, a very compact freeform lens with the lens center height equal to source size, is designed as the light distribution lens of a direct-type backlight. The simulation results indicate that the uniformity reaches 0.91, the relative standard deviance (RSD) is small to 0.0202 and the energy efficiency can reach 85.5%.