Abstract: In the free-form surface construction process, the solution deviation is produced, which will lead to the poor illumination performance of the traditional free-form lens. To make the illumination performance better and increase energy efficiency, a free-form lens design method based on the modulation of the aspheric inner surface was proposed. The aspheric inner surface was used to modify the deviation of the free-form surface. With a proper aspheric inner surface, the expected illumination performance was obtained and the energy efficiency was increased. By calculating the deviation of the free-form surface, the relationship between the incident ray and the slope of the inner surface was built. Taking an LED street light as an example, by using the method, the uniformity of illumination improved from 0.66 to 0.73, and the light usage efficiency is improved from 47.3% to 63.2%.