The so-called narrow-band optical imaging, which has been put into clinical use internationally only in the last two years, is an optical image emphasis technique that optimizes the central wavelengths to 415 nm and 540 nm for the observation of light strongly absorbed by blood and strongly reflected and scattered light on the mucosal surface, and narrows its spectral range to emphasize the mucosal surface vessels, fine structures of the mucosa and areas of capillary concentration. The NBI technique enables observation of the mucosal surface layer at high contrast, especially the fine structures that are important for the diagnosis of early gastric cancer. When patients visit the endoscopy center, patients with suspected early gastric cancer need to undergo stained magnification endoscopy and NBI endoscopy to determine the size of the lesion, give a pathological diagnosis of mucosal biopsy, and apply the C-13 breath test to determine whether H. pylori infection is present. When the diagnosis of gastric cancer was confirmed, ultrasound endoscopy was performed to clarify the stage of tumor infiltration and perigastric lymph node metastasis, and a multidisciplinary discussion was held to formulate a plan in combination with CT results. Patients with lesions invading only the mucosal layer and no lymph node metastasis can be treated radically by submucosal dissection of the mass under endoscopy without opening the abdomen.