Mid-infrared imaging devices， especially those operating in the atmospheric window （3-5 μm and 8-12 μm）， have important applications in infrared imaging and detection. Traditional mid-infrared imaging devices are usually bulky， expensive and complicated， which hinder the development of lightweight and integration in the future. The metalens， which are composed of subwavelength micro-nano structures arrayed in a periodic or aperiodic manner， have the characteristics of thinness， easy of integration and multi-functionality， providing new possibilities for future miniaturization needs. In this paper， the research progress of metalens in the mid-infrared band is reviewed， then the basic phase control methods of the metalens and its mechanism for achieving high focusing efficiency， eliminating chromatic aberration and monochromatic aberration in the mid-infrared band are introduced. Moreover， this paper sort out the imaging applications of mid-infrared metalens， including polarization dependent imaging， tunable and reconfigurable imaging and other imaging applications. Finally， the challenges and future prospects of this emerging field are discussed.