To study the thermal effort on optical properties of spatial heterodyne spectroscopy (SHS), the relation between the change in temperature and the degradation of optical properties was analyzed, including collimator lens, imaging lens and interferometer unit. The theoretical model was verified and corrected by simulation and thermal-optical test, which was established to describe the relation between spectral-line shift and groove density change of gratings. The results show that spectrum measurements are not affected by small temperature changes in the instrument since the primary effects are a slight defocus of the focal plane array in collimating lens and re-imaging lens under the temperature from 15 to 25 ℃. Spectral-line shift obtained by the thermal optical analysis is well coincident with the ones calculated by thermal optical experiment because of the temperature changes of interferometer unit. The Littrow wavelength accuracy is better than 2.3 nm unless the temperature change is less than 2.5 ℃ under the interferometer unit by use of the material BK7.