Portal venous gas (PVG) is an imaging sign of abnormal accumulation of gas in the portal vein and its intrahepatic branches due to various causes and is usually diagnosed by abdominal radiographs. It is commonly seen in neonates with necrotizing small bowel colitis. Necrotizing small bowel colitis is a serious disease characterized by abdominal distention, vomiting and blood in the stool, and cystic gas accumulation in the intestinal wall. 90% of the cases occur in premature infants, and the mortality rate is as high as 86% in those with both gas accumulation in the intestinal wall and gas accumulation in the portal vein. The cause of necrotizing small bowel colitis has not been fully elucidated, but it is generally believed to be caused by a combination of causes, of which prematurity and infection are the most important. 1, prematurity prematurity is an important pathogenic factor of NEC, due to poor immune function, poor intestinal motility, coupled with the ease of asphyxia at birth, resulting in hypoxic damage to the intestinal wall, allowing bacterial invasion. 2, Infection Infection is one of the main causes of NEC, mostly Klebsiella, Escherichia coli, Pseudomonas aeruginosa and other intestinal bacteria. 3, hypoxia and ischemia in neonatal asphyxia, respiratory diseases, shock and other hypoxic-ischemic conditions when the intestinal wall vasoconstriction, resulting in intestinal mucosa ischemia and hypoxia, necrosis, with the restoration of oxygen supply, vascular expansion and congestion, reperfusion during expansion will increase tissue damage. 4, feeding feeding and exchange transfusion can increase the reperfusion of the intestinal wall, which becomes a cause of disease and leads to bacterial attack on the intestine. Once feeding is started,it provides sufficient substrate for intestinal bacterial colonization. Intestinal feeding has been considered to be a factor in the pathogenesis of NEC, and premature and excessive feeding of cow’s milk in infected and asphyxiated preterm infants can induce NEC. but the view that feeding leads to NEC remains controversial, with some reports that the incidence of NEC in preterm infants delayed to 2 weeks from the start of feeding is instead higher than in those who are fed early. 5. The incidence of NEC is higher in other conditions such as umbilical artery or venous cannulation, blood exchange therapy, erythrocytosis, open arterial ducts, and hypothermia.