Compared with the medium-wave Infrared (MWIR) zoom optical system, the long-wave infrared (LWIR) zoom optical system has fewer available materials and is difficult to athermalize in high and low temperature environments. In this paper, the multi-field zoom optical system is realized by using mechanical compensation zoom technology, and the active compensation athermalization technology is used to make the system image clear in the temperature range of -40 °C—+65 °C, to realize the design of the four-field LWIR optical system with four lenses. The focal lengths of the four fields of view are 25 mm, 109 mm, 275 mm and 400 mm, the zoom ratio is 15, the envelope size of the optical system is 280 mm (L)×200 mm (W), and the total weight of the optical components is 618 g. The optical system has SWaP-C characteristics such as light weight, high performance, and low cost, and will be widely used in security fields such as auxiliary navigation, search, and tracking.