In our practice of treating esophageal achalasia with tunnel technique, we found that the morphology of the esophageal lumen greatly affects the establishment of a submucosal tunnel in the esophagus especially in patient with esophageal achalasia, so we reviewed the characteristics of the morphology of the middle and the lower parts of the esophagus in patients with esophageal achalasia, which included three endoscopically detected intraluminal structures: multi-ring structure, crescent-like structure and diverticulum structure, and finally proposed an endoscopic classification of esophageal lumen. This new classification was named Ling classification. The morphology of the esophageal wall is a key point during carrying out of tunnel technique, because it affects complications of tunnel technique. Although the Ling classification was initially proposed to characterize the esophageal wall of patients with esophageal achalasia, the main purpose of this classification is to assist in investigation of the indications and contraindications of esophageal tunnel technique. With the extensive development of tunnel technique, the Ling classification can be used to characterize the esophageal lumen for the side wall that targeted for tunnel establishment.