The presence of free gas under the diaphragm on examination is a sign of perforation of the gastrointestinal tract. In normal people, there is no free gas under the diaphragm, it is in a confined environment. When there is perforation of the stomach and intestine, the gas in the gastrointestinal tract, which runs out of the abdominal cavity and overflows into the diaphragm, manifests as free gas under the diaphragm. When there is this disease, it is necessary to further understand whether there is stomach pain, abdominal pain and the location of the pain to clarify whether it is a perforation of the stomach or intestine. If there is a history of peptic ulcer originally, it is considered to be a gastric perforation or duodenal perforation, and gastric repair needs to be performed as early as possible. If there is a history of intestinal ulcer, the perforation caused by ulcerative colitis needs to be excluded and surgical treatment is required.