According to sun radiometer radiance calibration method and process applied to China aerosol robot sun photometer network (CARSNET) work, the characteristics and technical requirement of sun radiometer radiance calibration in lab are analyzed. To fill up the blank sun radiometer sky diffuse channels radiance calibration of short wavelength, and to improve retrieved aerosol accuracy, the LED reference light source for sun radiometer sky diffuse channels radiance calibration is designed. The test results show that the planar uniformity of the source is better than 99.9% at the 20 mm exit normal circular area, the angular uniformity is better than 99.9% within ±2? to the exit normal, and the stability of source is better than 99.8% within 2 h. The LED reference light source satisfies the requirements of sun radiometer short wavelength diffuse channels radiance calibration.