A high zoom-ratio zoom structure type is introduced, which is composed of zoom imaging group and zoom reimaging group. The zoom ratio of system is the product of the two zoom groups. The size and numerical aperture of the intermediate image plane can be changed in the zoom process, when system is in short focal length position, the height of the immediate image is large while the numeric aperture is small. When system is in long focal length, the height of the immediate image is small while the numeric aperture is large. This will help to correct aberrations of image. Compared with the traditional zoom system, this type of zoom system structure is easier to obtain high zoom ratio. Using this structure a 80× cooled long-wave infrared zoom system is designed. The modulation transfer function (MTF) is above 0.26 in all focal length at the spatial frequency of 14 lp/mm. The result indicates that the structure can be used to achieve high zoom ratio zoom system.