The internal background radiation of the infrared spectrometer has a significant effect which will seriously reduce the resolution and signal-to-noise ratio of the optical system in the long-wave infrared band(8-12 μm). In this paper, the TracePro optical analysis software was used to analyze the background radiation of the cross asymmetric Czerny-Turner (C-T) type planar waveguide infrared spectrometer, including the surface emissivity of the mechanical components and the influence of the surface temperature of the optical elements on the background radiation. The stray light coefficient was introduced as the evaluation indicator, and the actual measurement was carried out before and after the background radiation suppression of the spectrometer system in the high and low temperature box. The experimental results show that the stray light coefficient of the spectrometer system can reach less than 5% under the normal temperature (298 K) after the background radiation suppression measures are taken.