Drinking water before gastroscopy is not allowed because when the subject undergoes gastroscopy, the fiber catheter will cause contact irritation to the epiglottis and esophagus, which may lead to reflex nausea, vomiting, acid reflux, heartburn, etc. Drinking water prior to the gastroscopy will exacerbate the extent of such adverse symptomatic reactions. Drinking water prior to gastroscopy can cause water to pool in the stomach, making it impossible for medical personnel to clearly visualize the internal structures of the stomach and adversely affecting the accuracy of the test results. Under normal circumstances, subjects try to maintain a light dietary regimen two days before undergoing a gastroscopy, avoiding spicy, cold, greasy and other irritating foods. No food and water should be consumed in the first 12 hours to avoid affecting the smooth progress of the gastroscopy. Maintaining a relaxed mood during the examination will help reduce the occurrence of adverse symptomatic reactions.