Based on the imaging characteristics of the infrared target simulator,a wide field-of-view (FOV) medium-wave infrared heat dissipation differential optical system was designed taking the improved Cooke type system as the initial structure.The optical system has an FOV of 30°,an exit pupil of 300 mm,an maximum diameter of 220 mm,and the focal length of 240 mm.Based on the principle of optical passive athermalization,a piece of aspheric lens is used.By choosing appropriate glass and focal power,the lens has an MTF superior to 0.4 under the environment of -40~60 ℃ at spatial frequency of 16 lp/mm,and also has good thermal stability and imaging quality,simple structure,and very strong practicability.