In order to improve the frequency and precision of radiometric calibration, the automated vicarious calibration system (AVCS) is developed and deployed at the Dunhuang test site to perform vicarious calibration without the in situ manned measurements. The surface and atmospheric parameters are automatically collected by AVCS. An absolute radiometric calibration approach based on AVCS is proposed. Six successful calibrations of the Aqua Moderate Resolution Imaging Spectroradiometer (MODIS) are conducted. The results are in good agreement with the on-board calibration system with all the relative differences less than 4%. It enables us to monitor the change of a sensor over long time scales.