Abstract: Cryogenic lens is usually used to detect faint point targets in deep space and low temperature environment. Encircled energy is an important index for evaluating such lens. An infrared cryogenic lens with thermal unloading structure was used as the test object. A test and error analysis scheme of encircled energy of cryogenic lens was designed. A point target was received after imaging by the lens and a cryogenic precision focusing technology was used to acquire data. Centroid extraction and Gaussian curve fitting and deconvolution had been applied to data processing. Encircled energy test was implemented of infrared lens at 200 K, and errors of the test system were analyzed and calibrated. Uncertainly analysis was also evaluated to improve the test accuracy. The experimental results show the test accuracy is better than 7.5%. The method can be used in engineering application.