Because the nephograms of FY-2 meterological satellite show that there exists stray infrared light in the radiometer, it is necessary to further modify the optical system used in the radiometer so as to suppress the stray infrared light. The generation mechanism and path of the stray infrared light in the optical system are simulated and analyzed by the TracePro software. On the basis of the analysis result, several measures which can be used to suppress the stray infrared light of the optical system effectively are proposed. Finally, these measures are evaluated by calculating the Point Source Transmission (PST) function of the optical system.