To overcome the disadvantage of the system uniformity reduction when a freeform surface constructed on the point source assumption is applied to the extended sources systems, a new feedback optimization algorithm based on the partial differential equation was proposed. Based on the point approximation, the initial surface structure were obtained through the numerical solution of the partial differential equation under the establishment of the radiation model of the extended light source. Then the shortcoming of the initial surface structure was analyzed when used for uniform illumination with extended sources under the circumstance that the rays transmission direction and the optical axis intersect. Therefore the proposed algorithm re-optimized the reflector to improve the uniformity by renewing the distribution of the target region, with the illuminance distribution in last simulation experiment as feedback. To illustrate the effectiveness of the proposed method, simulation experiments were carried out with TracePro. An extended light source with the size of 3 cm in diameter was used in experiments, in which total five million rays were computed. The light tracing experiments show that the uniformity of the object region increases from 60% to more than 90%, which demonstrates that the feedback design method can improve the illumination uniformity of the target surface effectively and provide some theoretical guidance for the improvement of the realistic lighting systems.