A method is proposed to design a freeform surface profile, which can make the illumination uniformity of the target surface location be a constant and can be used in the diffuse reflection surface indirect illumination system. Based on the ideal diffuse reflection freeform surface and light emitting diode Lambertian characteristics, equations of target plane illuminance distribution function are derived. The surface profile data is obtained by solving the equations. The diffuse reflection freeform surface is obtained by rotating around the axis. According to the illumination of the target surface, the evaluation function is built to optimize the solution of the array spacing. The non-sequential ray tracing simulation of the system is carried out by using TracePro software. The simulation results show that the target surface size is 50 mm circular area, the illumination distance is 200 mm under the indirect illumination of diffuse reflection freeform surface, the uniformity is 91.5%, and the effectiveness is 6.73%. Indirect illumination and direct illumination at diffuse reflection freeform surface for space optimized linear array, circular array and rectangular array are compared. Illumination uniformity of diffuse reflection freeform surface indirect illumination is better than that of direct illumination. The simulation results verify the correctness and effectiveness of the scheme.