Early manifestations of portal pneumoperitoneum are mainly paralytic intestinal obstruction: the small intestine is disorganized, the inflation is obvious, and multiple fluid levels are visible in the intestinal lumen in a stepped pattern. If the disease progresses and the intestinal gas enters the intestinal wall, cyst-like pneumatization of the intestinal wall appears. In the more severe cases, the portal vein is inflated because the intestinal gas enters the portal vein: the liver can be seen as a strip or dendritic translucent shadow from the hepatic portal to the liver along the portal vein, and in severe cases, the intestinal collaterals are fixed (intestinal necrosis), pneumoperitoneum (intestinal perforation), and peritoneal fluid (peritonitis). Cystic pneumatosis of the intestinal wall and portal vein inflation signs are the characteristic features of the disease. The differential diagnosis needs to be made between the following diseases: 1. Toxic intestinal paralysis: When the primary disease is diarrhea or sepsis, it is easy to misdiagnose NEC as toxic intestinal paralysis. However, there is no blood in the stool in toxic intestinal paralysis, and there is no air accumulation between the intestinal walls on the x-ray. 2, mechanical small bowel obstruction: X-ray abdominal film, the span of the fluid surface is larger, the intestinal wall is thinner, there is no widening of the intestinal gap, blurred, no intestinal wall gas, and then combined with the clinical is easy to distinguish. 3, intestinal torsion: mechanical intestinal obstruction symptoms are heavy in intestinal torsion, vomiting is frequent, abdominal X-ray plain film shows duodenal obstruction image, abdominal density is uniformly deepened, and there is irregular polymorphic gas shadow, no obvious inflation and dilatation of intestinal curvature. 4, congenital megacolon: early NEC should be differentiated from congenital megacolon when it shows generalized distention of the small and large intestines. The latter is dominated by abdominal distension and difficulty in defecation, without bloody stools. x-ray dynamic observation of abdominal changes without signs of pneumatization of the intestinal wall, combined with clinical easier to distinguish. 5, neonatal hemorrhage: 2 to 5 days after birth can appear gastrointestinal bleeding as the main manifestation, need to be distinguished. Neonatal hemorrhage has no history of vitamin K injection after birth, no abdominal distension, no intestinal cavity inflation and pneumatization of the intestinal wall on abdominal X-ray, and vitamin K treatment is effective. 6, meconium peritonitis: scattered small vesicle-like intestinal wall pneumatization can occasionally be seen on abdominal radiographs of individual cases, but there can be typical abnormal calcification shadows, and then combined with the clinical is not difficult to distinguish. 7, spontaneous gastric perforation: mostly due to congenital gastric wall muscle layer defects, often occurring in the gastric greater curvature near the cardia, most of the children have a history of hypoxia at birth. Sudden onset, 3-5 days after birth suddenly progressive abdominal distension, accompanied by vomiting, dyspnea and cyanosis, X-ray plain abdomen only see pneumoperitoneum, no intestinal wall pneumatization or intestinal tube distension.