Endocytoscopy (EC), as a kind of endoscope with ultra-high magnification, enables the in vivo observation of stained nuclei directly, which is of great significance for the diagnosis of early-stage cancer. Only Olympus of Japan has the technology so far. The core component of EC is the optical imaging system at the tip, and the current endocytoscopic imaging system has a small field of view (FOV) during imaging at high magnification, which leads to low efficiency. In this study, an endocytoscopic imaging system with high magnification and a large FOV has been proposed. We use six-piece spherical system to realize a zoom endoscopic objective lens with a large FOV, which has merits of high performance and low cost. Then, we construct the endocytoscopic imaging system based on this lens. The experimental results show that the object resolution of our system arrives at 181.0 lp/mm, and the magnification is about 500×. In addition, the FOV of microscopic imaging is significantly increased to 1200 μm×670 μm, which is more than double that of the current endocytoscopic imaging system. On this basis, the nuclear segmentation function is added to the system by deep learning, and the segmentation accuracy reaches 96.58%, which verifies the imaging ability of our system for the details of nuclear morphology.