In conventional microsurgery, the existing endoscope has the problem of a short working distance, is unable to achieve optical zoom, and is unable to obtain stereo images. Therefore, the design scheme of a two-path configuration 3D exoscope optical system with a long working distance and optical zoom features is proposed. The single optical path is composed of the front zoom system and the rear zoom system. The front zoom group system selects the three-element structure of optical compensation, and its function is to realize variable working distance and variable field of view while keeping the output light parallel. The rear zoom group system selects the four-element structure of mechanical compensation, and its function is to receive the parallel light of the front group system and keep the image plane position and image height unchanged. The combined optical system can achieve a zoom effect through the form of three moving group linkages. This solution is analogous to a microscope with infinite tube length. The parallel light path in the middle makes it easy to install and flexibly insert the beam splitter. Furthermore, the relation equation between the focal length of the front zoom system and the working distance of the object is derived. Based on the high-definition CMOS with a pixel number of 1920×1200 and a pixel size of 4.8 μm×4.8 μm, we design a six-switched 3D exoscope optical system. The object resolution of the system is 6.8-31.8 μm, the object field of view is 15-70 mm, the working distance is 180-380 mm, and the demagnification 1/β is 1.36×, 2.36×, 3.36×, 4.36×, 5.36×, 6.36×. By selecting a reasonable tolerance range, the design results show that the six-switched optical system MTF is better than 0.15 at 105 lp/mm with a probability of more than 90%, and the cam curve is smooth, which can meet the requirements of microsurgery.