Gastroscopy, as a conventional examination for gastrointestinal tract disease, plays a very important role especially in early diagnosis and differential diagnosis of esophageal and gastric carcinoma. However, conventional gastroscopy is associated with several adverse effects (including throat discomfort, breath-holding, nausea, vomiting, laryngeal spasm and increased heart rate) due to which some patients are intolerant to this examination or even refuse the procedure due to fear of these effects. Recently, painless gastroscopy has been applied increasingly widely in outpatients to meet the increasing needs for comfortable medical care.