Narrow Band Imaging (NBI) is an emerging endoscopic technique that uses filters to filter out the broadband spectrum of the red, blue and green light emitted by the endoscopic light source, leaving only the narrowband spectrum for the diagnosis of various diseases of the GI tract. The morphology of the epithelial vascular network can be observed. This new technology can better help endoscopists to distinguish the epithelium of the gastrointestinal tract, such as the intestinal chemosis epithelium in Barrett’s esophagus, the change of vascular morphology in the inflammation of the gastrointestinal tract, and the irregular change of the glandular recess of early gastrointestinal tumors, thus improving the accuracy of endoscopic diagnosis, improving the detection rate of early gastrointestinal tumors, and enabling patients to be diagnosed and treated at an early stage. 1. Background of narrow-band imaging technology. The traditional electronic endoscope uses a xenon lamp as the illumination light, and the broadband spectrum called “white light” is actually composed of three types of light, R/G/B (red/green/blue), whose wavelengths are 605nm, 540nm, and 415nm respectively. The narrow band light waves penetrate the mucosa of the gastrointestinal tract at different depths. The blue band (415 nm) penetrates shallowly, the red band (605 nm) can reach deep into the submucosa and is used to display the submucosal vascular network, and the green band (540 nm) can better display the blood vessels in the middle layer. Since the optical properties of blood in the mucosa absorb blue and green light more strongly, the use of light waves that are difficult to diffuse and can be absorbed by blood can increase the contrast and clarity of the mucosal epithelium and submucosal blood vessels. Therefore, NBI has the efficacy equivalent to mucosal staining, and the application only requires key switch without spraying stain, so it is called electronic staining endoscopy. 2.Narrow band imaging clinical application. Endoscope with NBI function has the same appearance and routine operation as ordinary endoscope, and can be switched to NBI mode to observe lesions at any time during operation. For the zoom magnification endoscope with NBI function, the NBI mode can be turned on after the close magnification observation of the lesion, so that the mucosal fossa pattern and blood vessels on the surface of the lesion can be understood more clearly, which is convenient for the characterization and targeted biopsy of the lesion. Currently, the applications of NBI in clinical work include: (1) early detection and diagnosis of microscopic lesions; (2) combined with magnified endoscopy to observe their fine structure, further evaluate their characteristics and predict histopathological results; and (3) as a means of targeting biopsy and endoscopic treatment of lesions. The application of NBI technology has greatly improved the diagnosis and detection rate of early cancers of the middle and lower pharynx, esophageal intraepithelial cancer, Barrett’s esophagus, early gastric cancer, and early colon cancer. The color contrast ratio between blood vessels and mucosa in NBI images is significantly greater, which makes it easier to observe and evaluate the morphology of esophageal epithelial microvessels (IPCL), especially for inexperienced endoscopists to detect lesions. The accuracy of the evaluation of IPCL using NBI endoscopy in predicting the depth of tumor infiltration is up to 85% compared with the histological gold standard, and therefore, the Japanese Society of Endoscopy recommends the routine use of HR-NBI in the screening of esophageal squamous carcinoma.