8～12 μm infrared (IR) hybrid refractive continuous zoom lenses are designed, based on long-wave 160×120 element uncooled thermal IR focal plane arrays (FPA) detector. The continuous zoom system has a large relative aperture, the F#=1.1, high zoom ratio, smooth curve of zoom. Two common infrared materials of Ge and ZnS are used in this optical system. To correct off axis aberration, aspheric surface is accepted, zoom ratio can be improved by solving compensated curves at the middle equivalent focal length,and the optimum design of cam curve has brought the optical axis drift under control in the process of zoom. The modulation transfer function (MTF) is above 0.55 in all focal lengths at the spatial frequency of 17 lp/mm and approaches the diffraction limit.The energy permeance ratio is greater than 78% within the detector sensor limits smaller than17.5μm, which shows that the optical system has good imaging quality.