According to the theoretical model of continuous zoom optics, the continuous zoom calculation program is compiled, the initial solution of the zoom system is obtained, and the paraxial optical model is established. Through material selection and iterative optimization, a midwave-infrared continuous-zoom optical system consisting of only four infrared lenses and two planar mirrors was realized. The F number of the system is 4, the spectral range is 3.7.to 4.8 .m, the field of view (FOV) is 20°×16°.to.2.0°×1.6°, and the maximum aperture of lenses is 71.0 mm, the total weight of the lenses is 64 g, and the system envelope is 172 mm×108 mm. The system uses two binary surfaces for the achromatic. The athermalization design of the system was realized through the rational allocation of materials and active compensation. The medium wave infrared continuous zoom optical system has the advantages of light weight, short total length, small envelope, and good image quality in the temperature range of -40℃.to 60℃.