In recent years, with the continuous development of optical technology, infrared systems have become the focus and hot spot of research from all walks of life and have a wide range of applications in military and civilian fields. However, these fields have extremely high requirements for the imaging quality and environmental adaptability of lenses. Long-wave infrared usually refers to the 8-12 μm region in the infrared spectral range, which covers the main wavelength band of thermal radiation of objects at room temperature, with a wide wavelength range, which can capture infrared radiation with a longer wavelength. The influence of temperature changes must be considered in advance before the design of the optical system in this wide wavelength band, and the athermalized design of the optical system plays a crucial role. In optical system design, due to the imperfect nature of optical components, heat is generated and leads to a series of problems, such as focal distance shift, optical distortion, spot diffusion, etc. In order to solve these problems, the athermalized design of the optical system came into being. The key to a thermal-free design is to minimize the effects of heat throughout the design process and to ensure that the optics maintain a stable temperature and good image quality during operation.In order to keep the performance of the infrared system stable at different temperatures, thereby reducing or eliminating aberrations and image quality degradation due to temperature changes. In this paper, the combination of optical passive athermalized and mechanical passive athermalized is used to design a long-wave infrared system with a large field of view. The optical system adopts the refractive structure, firstly, the designed infrared system is designed with optical passive athermalized, and its imaging quality is analyzed, if the imaging quality is not ideal, the mechanical design is carried out based on mechanical passive athermalized to improve the imaging quality.The working band of the system is 8-12 μm, the focal length is 45 mm, and the F-number is 1, and it can work stably in the temperature range of -40-65. At the cut-off frequency of 42 lp/mm, the MTF is greater than 0.3 on the axis and greater than 0.25 on the axis, and the MTF is not much different at different temperatures, and the imaging quality meets the requirements. The RMS radius at different temperatures is not much different and the imaging quality is good, which meets the design index. The distortion of the system is less than 2% at room temperature, which meets the design index. And the tolerance analysis of the optical system was carried out, using the Monte Carlo analysis method, the tolerance calculation mode was sensitivity, and the diffraction MTF was averaged, and 500 simulations were carried out to obtain the tolerance analysis in the case of -40, 20 and 65, and the analysis results showed that the system performance was good and met the design requirements.The system adopts the combination of optical passive athermalized and mechanical passive athermalized, that is, hybrid passive athermalized, and designs a large field of view long-wave infrared optical system. The operating band is 8-12 μm, the F-number is 1, the focal length is 45 mm, and the working temperature is -40-65 ℃. The imaging quality of the system is good, the performance of the system is stable at different temperatures, and the tolerance range meets the actual processing needs. For the use of hybrid passive athermalized design method, if only optical passive athermalized needs to consider the characteristics of multiple materials, and the design can only be carried out by reasonable allocation of optical lenses, which is more complicated. The mechanical passive athermalized design also needs to understand the characteristics of a variety of structural materials, and the mechanical structure design is more complex, so the hybrid passive athermalized design is used to design, the optical design is relatively simple, and the structure is relatively miniaturized.