The patient is a 40-year-old female. She had been suffering from acid reflux, heartburn and abdominal pain for 20 years, aggravated by vomiting for 1 month. 20 years local hospital gave gastroscopy and upper gastrointestinal barium meal imaging to diagnose esophageal hiatal hernia, reflux esophagitis and duodenal bullae, and gave omeprazole and other treatments for improvement. The symptoms worsened and vomiting appeared in the month before admission. Gastroscopy at the local hospital still diagnosed “reflux esophagitis”, which was poorly treated, and the symptoms got worse. Gastroscopy was repeated: the duodenal bulb descending junction was stenosed, the scope could not pass through and the lesion could not be seen, and a guide wire was applied to penetrate the scope into the stenosis under guidance. Tissue biopsy was taken from the stenosis and pathological diagnosis of hypofractionated adenocarcinoma was made. It suggests us that endoscopy should be done carefully and improve operational skills to diagnose correctly and early to avoid delaying treatment, especially for malignant tumors.