Aiming at issues such as blade ablation, carbon deposition, and damage in critical components of aviation engines, including compressors, combustion chambers, and turbines, which result in pits, cracks, and other defects, a long working distance, small-diameter binocular measurement borescope is designed to measure these damages based on the principle of binocular stereoscopic measurement to determine the specific extent of pits, cracks, and other damages on the blades to guide repair processes. The designed borescope consists of an objective lens, an image-inverting rod lens group, and a dual-telecentric single-pass posterior objective lens that images onto two areas of 2/3 inch in image sensor. This borescope features a long working length and a small diameter, making it suitable for aviation engines, such as the CFM56 series. Considering manufacturing and assembly tolerances, the borescope meets the requirements after thermal stabilization and tolerance analysis. The optical system has a length of 570 mm and full field of view of 72°. At a measurement distance of 40 mm, the object side resolution is 6.33 lp/mm, angular resolution is 4.59 cycle/(°), and modulation transfer function exceeds 0.35@50 lp/mm, approaching the diffraction limit. The telecentricity is not more than 0.8°, single optical path diameter is not more than 2.8 mm, and overall diameter is not more than 8 mm.