The influence of the temperature on infrared continuous zoom system will lead to the change of zoom curve and complex focusing compensation,so an athermalization method is presented through analyzing the relationship of every component in the system when temperature changes. Through local athermalization design of zooming group and compensation group,the temperature influence can be compensated by linear shift of zooming group and compensation group without changing the zoom curve,which reduces the controlling difficulty of focusing mechanism. A mid-infrared continuous zoom optical system with 12 zoom ratio is designed by this local athermalization method. Only using one zoom curve,the MTF of about 0.3 at 30 lp/mm is achieved when focal length range is from 25 mm to 300 mm and all the temperature range is from -45 ℃ to 50 ℃,which nears the diffractive limit. The system has the advantages of continuous zoom,high zoom ratio,zoom curve athermalization,high image quality,simple structure and so on.