Differential optical absorption spectrometer is a spaceborne optical instrument with precision mechanical structure aboard GF-5 satellite, and there are high temperature stability requirements to the optical-mechanical system and the detector throughout its life cycle. In order to ensure the accuracy of the optical path, the optical installation plate temperature gradient needs to be less than 2℃. In order to reduce the interference of temperature fluctuation to the signal, the temperature fluctuation within whole track is required less than 2℃. Locating with several payloads around, the thermal environment is complex, which makes the design of thermal control difficult. In combination with the thermal control requirements and structural characteristics of the spectrometer, the thermal flow outside on the orbit is analyzed in detail. The side toward earth is used as a heat dissipation surface. The isothermal design is applied for the optical bottom plate. The sunward surface of the instrument is taken as an electronic heat dissipation surface. Some measures are performed to keep the heat insulation between electronic box and optical box. The high stability of temperature control for the spectrometer is realized. The thermal balance test and on-orbit data show that the thermal control design of the spectrometer is reasonable and feasible, and can meet the temperature index demand for on-orbit detection. It builds a good foundation for the high-precision and high-stability thermal control design of the follow-up optical remote sensing instruments.