In a cooled infrared optical system, the cooled detector can be reflected through the front optical surface, such that the detector can detect its own reflecting image. The phenomenon of a dark spot with a bright edge and a dark center is called "Narcissus," which has a significant influence on image nonuniformity of the cooled infrared optical system. Narcissus should be strictly controlled in the process of optical design. In this study, a medium wavelength infrared optical system is taken as an example and a technical approach is proposed to effectively solve or reduce narcissus. A non-sequential mathematical model was established based on ZEMAX optical design software and simulation was conducted for analysis. The narcissus of the optical system was reduced from 40% to 13% after optimization and an engineering prototype imaging experiment was conducted. The analysis results of the simulation were consistent with the experimental phenomenon. This analysis method can accurately reflect the actual situation of Narcissus and can be used as a basis for judgment before the development and production of a cooled infrared optical system.