The structure layout of one space gas monitoring sensor is very compact. There are eight optical lens, eleven electronic devices and two motors staggered in the small-scale space. There were so many calorific equipments with long working hours and large power consumption, and their temperature control requirements were not consistent with the optical lens, the number of which was also large. Furthermore, one of the two motors was a two DOF turn motor during operating. These above characteristics make thermal design of the gas monitoring sensor a great challenge. To effectively solve the difficult problems of the gas monitoring sensor thermal design, combination of multy design methods were adopted. The thermal behavior of the gas monitoring sensor components were systematically managed based on the idea of thermal management to save thermal control resources. Indirect thermal control technology was used on the optical lens temperature control to guarantee meeting the high precision and stability requirement. Heat dissipation of the two DOF turn motor was achieved by radiation cooling, by which flexible rotating table could be avoided in the cooling path, so that thermal control system reliability could be improved. Finally, structural and thermal integrated design was applied to make sure the requirements of those above thermal design fully guaranteed in structure. The results of thermal balance test show that all components temperature meet the requirements no matter under cold case condition or hot case condition, and optical lens have high temperature stability throughout the life cycle. The maximum temperature fluctuation of all optical lens is less than 1 ℃ under the same case condition. High precision thermal control of optical lens are obtained under the condition of multiple heat source and complex working mechanism.