To ensure a proper averaged temperature and a temperature gradient of a space spectral imaging apparatus, the characteristics of thermal design for the space spectral imaging apparatus were discussed and analyzed. According to the design feature and the heat transfer path in the spectral imaging apparatus,a thermal design scheme for the apparatus was presented and the thermal equilibrium equation and a numerical analysis model of the heat transfer for the apparatus were established by finite element analysis method. Based on given temperature boundary conditions,the steady-state thermal analysis of the apparatus was carried out through a finite element thermal analysis software IDEAS-TMG. The thermal response performance and steady-state temperature profiles of key parts in the apparatus were given.Thermal analysis shows that the averaged temperature value and maximum temperature gradient value of the apparatus in steady-state are 17.3～23.7 ℃ and 1.3 ℃, which has met the requirements of heat control,and can supply a theoretical warrant for reliability and optimization of thermal design. Thermal design scheme was also verified through a thermal test and obtained results are well coincident with that derived from confirmatory test and numerical analysis. The maximum deviation between thermal analysis and thermal test are not exceeding 8%. The correctness of numerical simulation and the validity of temperature prediction were verified. In thermal test, the averaged temperature value and maximum temperature gradient value of the apparatus are 17.2～22.5 ℃ and 1.4 ℃,respectively.