Abstract: A low-cost and high-quality hybrid passive athermalization method for LWIR was proposed by combining passive optical and passive mechanical athermalization. An athermalization optical system with a focal length of 75 mm and F/1 was designed using passive optical and hybrid passive athermalization. Compared with traditional passive mechanical athermalization, the volume and complexity of the thermal compensation structure can be reduced using hybrid passive athermalization. In addition, the proposed method decreases the volume and weight of the system. Compared with passive optical athermalization, hybrid passive athermalization can reduce the volume and processing difficulty when the imaging quality is the same. Thus, the propose method can be used to achieve a low-cost, high-quality, long-wave athermalization system.