GF-5 satellite was successfully launched on May 9, 2018. It is the first hyperspectral observation satellite in China. The Greenhouse gas Monitoring Instrument is one of the payloads. It is the first satellite-borne greenhouse gas remote sensing equipment in the world to use spatial heterodyne spectroscopy technology for hyperspectral spectroscopy. The basic working principle of the payload was described, including the principle of light splitting, working mode and band setting. The optical system of the payload consisted of five parts. The core unit was a bonded interferometer. In order to avoid spectral aliasing, the parameters of narrowband filters were required to be high. In order to improve the on-orbit data quantification level, a calibration device based on diffuse reflector system was designed, which can meet the requirements of spectral and radiation calibration. Finally, the basic process of payload data processing was sorted out, and the first batch of observed data was restored by spectrum. The first-level data products are successfully obtained, which lays a foundation for the next application of greenhouse gas inversion.