In order to solve the technical problem of rapid performance degradation caused by radiation when using an infrared thermal imager in a high-radiation environment, based on the mechanical positive group compensation continuous zoom structure, the reflector is introduced into the rear fixed group to form a folding optical system, to avoid the back-end detector from the front radiation rays. An uncooled infrared continuous zoom optical system with an operating waveband of 8－12 μm, a F-number of 1.2, and a focal length of 25－90 mm is designed. The results show that the system has a reasonable structure and good imaging. The modulation transfer function (MTF) value at the characteristic frequency of 42 1p/mm corresponding to the detector is greater than 0.2, which meets the application requirements. After processing and adjustment, the accuracy of the design is verified by actual imaging test.