Based on the design of cooled infrared near range imaging system without focusing mechanism,the influence of the near range imaging system focusing on the narcissus phenomenon is discussed.The un-necessity of focusing mechanism in fix focus near range imaging system is analyzed,and the method of how to select suitable parameters to raise the depth of field and how to select materials to athermalization design is proposed for no focusing mechanism design.Based on medium-wave 320×256 focal plane array cooled detector,a athermalization infrared system with effective focus length 20mm,F/4 is designed.This system can work well in distance of 1~10 m and temperature of -40~55 ℃ without focusing mechanism.