Space-borne differential optical absorption spectrometer is mounted on the Sun-synchronous orbit satellite, which quantitatively monitors the global air quality changes and the transmission of pollutant gases distribution. The onboard calibration is the basis to obtain accurate quantified imaging data, and the space-borne instrument adopts sunlight calibration mode and standard lamp calibration mode. In order to ensure the reliability and accuracy of onboard calibration, analysis and rational design of the calibration mechanism are needed.