In this study, the simulation analysis and optimization of stray radiation in deep cryogenic Dewar components were conducted using a multiwave common optical path Dewar infrared system. The thermal radiation effects on the detector from key surfaces at different temperatures were analyzed using temperature field and dichroic surface simulations. Suitable cold transmission materials were selected, and Kovar was used for the cold platform, cold screen, and dichroic holder of the Dewar system. The effects of different blade levels and surface treatments of the cold screen on the point source transmittance were also evaluated. Based on these findings, the following optimization scheme was proposed: an elevated cold screen to block most of the radiation emitted or reflected by the window cap, adopting two levels of blades for the cold screen, and spraying graphene on the inner surface of the cold screen to improve the suppression of stray radiation. This scheme provides both theoretical and practical value for the design and application of low-temperature Dewar modules.