This disease is mainly due to vitamin K deficiency. The causes of vitamin K deficiency are: (1) Low blood levels and intrahepatic stores of vitamin K because vitamin K does not easily pass through the placenta in the pregnant mother. (2) Since the vitamin K content in breast milk is low and much lower than that of formula-fed children, breast-fed children are prone to vitamin K deficiency. (3) The synthesis of vitamin K requires the participation of intestinal bacteria, and newborns have few intestinal bacteria at birth, so they are prone to vitamin K deficiency. (4) Newborns with chronic diarrhea or on oral antibiotics for other illnesses have insufficient vitamin K synthesis due to reduced normal intestinal flora. (5) The absorption of vitamin K is affected when the newborn has liver and biliary diseases. (6) Phenytoin sodium, phenobarbital, bicoumarin, rifampin, isoniazid, etc. used by the mother before delivery can affect vitamin K metabolism. After vitamin K deficiency, coagulation factors II, VII, IX and X cannot be carboxylated, and the above coagulation factors that cannot be carboxylated do not have the biological activity of coagulation, thus leading to bleeding.