Gastric cancer is one of the most common malignant tumors with insidious onset and many patients are already in the progressive stage when diagnosed. Therefore, early diagnosis and treatment are crucial to improve the 5-year survival rate of gastric cancer. Endoscopic spectroscopy selectively processes the most clinically significant light wave information and is represented by narrow band imaging (NBI) and the Fujinon Intelligent Color Enhancement (FICE) system. Compared with pigmented endoscopy, endoscopic spectroscopy is easy to operate and can switch between stained and white light states, improving the contrast between lesions, microvessels and surrounding tissues, increasing the detection rate of superficial lesions, and playing an important role in the field of early gastric cancer diagnosis. Narrowband imaging In 1999, the National Cancer Center of Japan invented endoscopic narrowband imaging (NBI), which uses the principle that light of different wavelengths can penetrate the mucosa at different depths to image and reconstruct images using different wavelengths, such as observing the mucosal surface using 400 ~ 500 nm wavelengths and blood vessels using about 550 nm wavelengths. The specific principle of NBI is to filter the broadband light waves of white illumination used in conventional electronic endoscopy through a red, green, and blue (RGB) filter, leaving only the narrowband light waves of blue, green, and red at 415 nm, 540 nm, and 600 nm. Since the narrow band wavelengths are within the wavelength range of light waves that can be absorbed by hemoglobin and are difficult to diffuse, they can increase the contrast and clarity of the mucosal epithelial and submucosal vascular patterns, thus improving the accuracy of diagnosis. Different wavelengths of narrow-band light waves penetrate the mucosa of the gastrointestinal tract at different depths, with the blue band (415 nm) penetrating shallowly and being reflected by capillaries on the mucosal surface, making it appear brown; the red band (600 nm) can penetrate deeply into the submucosa and is used to show the collecting vessels in the submucosa, making it appear green; the green band (540 nm) has a penetrating ability between the above two light waves, penetrating The depth of the mucosa is 0.15~0.30 mm, which can better display the vessels in the middle layer. If NBI is combined with magnification endoscopy, the structural morphology of mucosal microvessels and glandular ducts can be clearly displayed, thus facilitating the determination of the nature of the lesion. Studies have shown that NBI is better than traditional endoscopy for the visualization of recessed lesions, better than traditional endoscopy for the visualization of mucosal vascular network and lesions, and has 100% sensitivity and 75% specificity for distinguishing tumorigenic and non-tumorigenic lesions, which is similar to and better than traditional endoscopy. Endoscopy Center of Beijing Cancer Hospital has the leading narrow band imaging technology in China, and dozens of patients with early gastric cancer have been diagnosed and treated under endoscopy with excellent results in short-term follow-up.