In order to solve the problem that the performance of infrared imaging system rapidly degenerate in high radiation environment，an uncooled infrared dual-field imaging optical system with a focal length of 30/120 mm is designed by “L” folding of the two-stage variable optical system for secondary imaging. The operating wavelength range is 8 to 12 μm， F number is 1.1. The design results show that the system has simple and compact structure， small volume and good imaging quality， so that its MTF value at the characteristic frequency 30 lp/mm corresponding to the detector is greater than 0.4. It can well meet the application requirements.