Automatic radiometric calibration is the latest development trend in the field calibration of satellites. Its core is to obtain TOA ( top of atmosphere) reflectance that can be compared with satellite observation data on a regular basis. This paper developed an on-orbit radiometric calibration method for satellites based on the TOA reflectance at the Baotou site. Firstly, the empirical model for TOA reflectance was built based on the long-time-series observation data from a high-precision reference satellite over the automatic radiometric calibration field. This model was used to correct the TOA reflectance of the automatic radiometric calibration field at other moments. Consequently, the uncertainty of TOA reflectance was reduced, and the accuracy of radiometric calibration was improved. The proposed method was validated and analyzed with Sentinel-2A/2B as the reference satellite and the TOA reflectance of sand targets at the Baotou site as the research object. The results show that the model built in this paper has high accuracy, and the average relative difference between the predicted values of the model and the observed values of Sentinel-2 is less than 2% (less than 3% in the blue band). With this model, the relative difference between TOA reflectance at the Baotou site and the actual TOA reflectance observed by Sentinel-2 can be greatly reduced and the inconsistency is decreased from 5%--6% to less than 3%. These results validate the effectiveness of the proposed method.