A large-scale in-door illumination simulating system was designed and developed by Beijing Institute of Spacecraft Environment Engineering for solar illumination test requirements of a deep-space sensor. Metallic Halide Lamps and Tungsten Halogen Lamps with good accuracy and small collimating angle lanterns, which are high-power and good-match with sunlight, distribute on the wall of the laboratory in order to make good uniformity in an area of 20m×20m. Design results show that, firstly, total average radiation intensity is 400.4W/m2. Secondly, intensity are 48.5W/m2 in 600nm～700nm and 5.1W/m2 in 965nm～995nm. Thirdly, incident angle of the system range from 15° to 45°. Fourthly, uniformity with 15°, 30° and 45° are ±12.4%, ±8.1% and ±14.9% respectively. Finally, shadow profile in the area is clear. The results of acceptance test match the design results very well and meet the requirements totally. The system has been used in laboratory test of the detector successfully.