The space-borne Fourier Transform Spectrometer carried by FY24 meteorology satellite is one of infrared remote sensing instruments. It acquires the temperature , pressure and humidity of atmosphere, and supp lies the valuable weather data for next numericalweather forecast. Based on the sounder’s structure, the internal radiance calibration by inserting a blackbody pick-off mirror is presented. The transmission on-orbit measurement of telescope and blackbody pick-offmirror is also discussed . Thismethod provides a new approach for the geostationary remote sensing instrument of next generation.