At present, optical remote sensors are developing in the direction of large aperture and wide field of view. With the increase of the remote sensor′s diameter and field of view, corresponding calibration devices need to be developed to meet the radiometric calibration requirements of full aperture and full field of view. Therefore, a ultra-large aperture (3.2 m) uniform light source system is developed. Firstly, the spectral radiance of exit aperture is designed based on the integrating sphere theory and Plank theory, and the LightTools software is used for the simulation design of the exit uniformity and Lambert properties of the built-in light source distribution. Then, a set of radiometric performance measuring devices based on multi-detectors is developed to solve the problem of ultra-large aperture uniform light source measurement. The calibration algorithm is applied to make multi-detectors consistent. Finally, the new device is applied in the testing experiment of ultra-large aperture uniform light source, and its test uncertainty is analyzed. The results show that the integrated spectral radiance of 0.8 m exit aperture is more than 600 W·m-2·sr-1, the spatial uniformity of 3.2 m exit aperture is more than 98.362%, and the Lambert uniformity in central point of ±45° is more than 98.810%. The newly developed ultra-large aperture uniform light source meets the design requirements.