Sunphotometer is the most important observation instrument in global AERONET site, which supply a lot of observation data for obtaining time and space distributions of global aerosol. A kind of high accuracy calibration method against cryogenic radiometer is developed in laboratory, calibration coefficient of sun channel and sky diffuser channel can be obtained in the ambient condition of laboratory. The calibration principle and installation are introduced in detail, calibration curve of absolute spectral responsivity are obtained in major spectral channel, and measurement uncertainty is analysed. The result indicated that the uncertainty of calibration coefficient of sky diffuser channel is less than 0.8% and sun channel is less than 2.06%.