Narcissus refers to the phenomenon in an infrared system where a cooled imaging sensor can “see” its own reflected image by the reflection of the frontal optical surfaces. Control of narcissus is one of the important requirements in the design of the infrared imaging system. A cooled medium-wave infrared imaging system with Cassegrain reflection structure is designed and analyzed to obtain the optical surfaces with serious narcissus. In addition, the narcissus is reduced by Zemax, and the optimization of the system transfer function MTF is taken into account while the narcissus is controlled. The optimized medium-wave infrared imaging system is compared with the imaging system without narcissus suppression through NARCISSUS macro (narcissus analysis macro), Tracepro modeling software and actual imaging, and it was found that the narcissus induced equivalent temperature difference (NITD) of the detector image surface decrease from 1.0484 K to 0.1576 K. The energy and size of the narcissus spot did not show marked change during the focusing of the system. The optimized optical structure can effectively control the narcissus of the system.