Endoscopic narrow band imaging 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 narrow band spectrum for the diagnosis of various diseases of the GI tract. the main advantage of the NBI technique is the ability to accurately observe not only the epithelial morphology of the GI mucosa, such as the structure of the epithelial glandular recess, but also the morphology of the epithelial vascular network. 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 recesses of early tumors in the gastrointestinal tract, thus improving the accuracy of endoscopic diagnosis. 1. early detection and diagnosis of microscopic lesions; 2. joint magnification endoscopy to observe their fine structure, further evaluate their characteristics and predict histopathological results; 3. as a means of targeting biopsy of lesions and positioning for endoscopic treatment. The application of NBI technology has greatly improved the diagnosis and detection rate of early cancers of the middle and lower pharynx, esophageal intraepithelial carcinoma, Barrett’s esophagus, early gastric cancer, and early colonic cancer.