Vomiting after drinking only water in late stage of lung cancer may be caused by tumor compression of esophagus, tumor metastasis, gastrointestinal dysfunction and so on. 1. Tumor compression of esophagus: if the tumor increases in size and leads to esophageal pressure, it may cause esophageal stenosis, which may lead to vomiting after drinking water only. 2. Tumor metastasis: if the tumor metastasizes to the brain, it may cause intracranial hypertension, and vomiting may occur when only drinking water. 3. Gastrointestinal dysfunction: if the use of chemotherapy and other drugs in the late stage of lung cancer leads to gastrointestinal dysfunction, it may cause symptoms such as loss of appetite, abdominal distension, vomiting and so on. It is suggested that patients should go to the hospital for consultation in time to clarify the cause of disease and carry out standardized treatment under the guidance of doctors.