To meet the radiometric calibration requirements of optical remote sensor with large aperture and wide viewing field, a spectrally tunable reference light source with 3-m diameter integrating sphere and 1-m diameter exit port is designed. By incorporating multi-wavelength light-emitting diode (LED) modules and tungsten-halogen lamps modules, both absolute radiance and spectral distribution of the light source can be adjustable within 400~2500 nm. A spectral auto-match algorithm is developed to generate solar, ocean, vegetation, desert and other typical target spectrum. LED modules are cooled by water circulating system with high temperature stability and driven by high precision programmable direct current power supplies, which ensures the stability of exit radiation. The test results show that the planar uniformity of the source is better than 99.5% at the exit port, the angular uniformity is better than 99.4% within ±60° to the exit normal, and the stability of source is better than 99.8% within 2 hours.