In order to design and manufacture integrating sphere radiation sources with high angular uniformity, it is necessary to provide optimized design parameters. Based on the radiative transfer theory of cavity, a simulation model of light exitance distribution of light-emitting unit based on cascaded integrating sphere structure was established, and the relationship between the installation position of the Lambertian light-emitting unit and the angular uniformity of the cascaded integrating sphere radiation source was obtained. The simulation results showed that, in ideal conditions, when two Lambertian cascaded sub-spheres were used as light-emitting units and were symmetrically installed at an angle of 10° with the normal direction of the light outlet of the cascaded integrating sphere radiation source, the angular uniformity in the observation area at an angle of ±20° between the center of the sphere and the normal direction of the light outlet could reach the level of 0.03%. Finally, the angular uniformity of the cascaded integrating sphere radiation source at the 30° angle position of the cascaded sub-spheres was measured experimentally, and the experimental results were close to the simulation results. Therefore, by optimizing the type and installation position of the light-emitting unit, the angular uniformity of the integrating sphere radiation source could be effectively improved.