In order to meet the urgent need of large-scale search and accurate target recognition， an infrared zoom imaging system with large zoom ratio is developed. Two independently moving zoom lenses and one compensating lens are designed， the large zoom ratio can be obtained by the cascade of two zoom lenses. According to the characteristics of multiple moving lenses and complex zoom curves， the zoom motion is realized by linear motion mechanism， and driven by linear motor integrated encoder and thread screw rod. The mechanical analysis of the system is carried out by the finite element simulation， and the maximum displacement of the lenses is 3.04×10^-3 mm. The imaging system is suitable for the medium-wave infrared cooled 640×512 focal plane area-array detector， and the zoom ratio is 55. The results of laboratory imaging and outfield imaging show that the system has a clear and good imaging quality with a continuous change in focal length from 6 mm to 330 mm， which verifies the performance of the system. The design is reasonable and reliable. The research findings of this paper have broad application prospects in search， tracking， reconnaissance， and surveillance.