Stray light is one of the most important factors that affect the image quality of optical system, thus the analysis and suppression of the stray light becomes a significant part in the design processes of the modern infrared optical system. According to the requirements of stray light, the configuration of the space-borne infrared optical system is determined; the sources of the stray light is analyzed, and then point source transmittance (PST) is taken as the standard to evaluate the analysis; the methods of the stray light suppression are designed, such as baffle, vanes, occulters, stops and material; the model of the system is established and its stray light is analyzed with TracePro, and then the PST curves of the system are calculated. The results indicate that the thermal emission of the system is 1.53×10-3 W/m2; the PST curves of the system are declining, at off-field angle ±3°, the PST of the system arrives at 10-3~10-5, stray light suppression of the system satisfies the requirements of the image quality.