On-orbit radiometric calibration of spaceborne differential optical absorption spectrometer can be conducted based on the bi-directional scattering distribution function (BSDF) and the sun. The EMI BSDF is the ratio of EMI radiance and irradiance calibration function. Radiometric calibration of observation path is completed on the ground. Radiometric calibration of calibration path can be realized by the sun. Then EMI BSDF is obtained, and the on-orbit radiometric calibration is conducted. The results between the EMI and TROPOMI show that the accuracy of the radiance calibration is 5%～6.5%.