Abstract: With the development of optical technology and modern medicine, the public acceptance of endoscope-based minimally invasive surgery is increasing. Doctors diagnose by observing the images of diseased tissues obtained from endoscopes, so the imaging quality of endoscopic optical systems is crucial. Most of the endoscopes currently on the market have clear images, but the details are not sharp enough. An endoscopic optical system with 2k resolution based on Zemax was designed to achieve better final image quality. By increasing the relative aperture of the objective lens, providing a new relay rigid lens optical system and matching adapter optical system, the entrance pupil diameter is 0.6 mm, the total length is 388.7 mm, the field of view is ±37.5°, the objective resolution is 32 lp/mm at an objective distance of 26 mm, and the objective angular resolution is 17/ c/(°). After considering the processing and assembly errors, the results of the tolerance analysis meet the actual use requirements.