Narcissus of cooled infrared system should be controlled strictly. So, accurate and rapid analysis of narcissus is very important. Deriving the SNR of narcissus based on the definition of noise equivalent power. Using simulation software CodeV and ASAP analyses the narcissus. Screen out the optical surface whose narcissus is serious in CodeV. Then build the model of the system in ASAP and add reasonable surface properties, get the result of size and average irradiance of the image narcissus spot by real ray tracing. Calculate the SNR of narcissus by putting the value of average irradiance into front formulation. On this basis, the simulation analysis and experimental test about the Narcissus of an infrared lens were performed. The experimental result is consistent with the simulation analysis.