To ensure the validity and reliability of the secondary inversion data of environmental trace gases monitoring instrument (EMI), it is necessary to monitor the radiometric calibration accuracy and stability of the instrument in orbit for a long time. First, according to the solar spectrum and sub star radiance data measured by EMI in orbit, the surface reflectance time series of the selected data area of permanent ice and snow surface in Antarctica and Greenland are calculated, and the fourth-order bidirectional reflectance distribution function (BRDF) model between the solar zenith angle and the surface reflectance is established. Then, the surface reflectance data series from 2018 to 2020 are normalized by the fourth-order BRDF model, and the indicators representing the calibration accuracy and stability of EMI are obtained. The results show that the correlation coefficient between the predicted value of surface reflectance obtained by BRDF model and the measured value is better than 0.9. After normalizing the surface reflectance with the BRDF model, the uncertainty of radiometric calibration ranges from 2% to 5%. The total attenuation of UV2 and VIS1 channels range from -5% to 5% in two years, and that of VIS2 channel is about 1.9%, which indicates that the radiation response of EMI is stable during two years of operation in orbit.