In this paper,a miniaturized middle wavelength infrared optical system is proposed,which is based on a three component linkage continuous zoom.An F number 5.5 middle wave infrared zoom lens with 20～275mm focal length is designed for cooled MWIR detectors with 640×512 array size and 15μmpixel size.The total optical length of the system is 90.6mm.The system has the characteristics of large zoom ratio,compact structure and less components.The designed system is suitable for applications in miniaturized pods systems,lightweight handheld infrared telescope systems.