It is a group of hereditary hemorrhagic diseases with severe coagulation disorder due to the lack of some coagulation factors in the blood, which can occur in both men and women, but most of the patients are men. Including hemophilia A (A), hemophilia B (B) and factor XI deficiency (once known as hemophilia C). The first two are sex-linked recessive inheritance, while the latter is autosomal incomplete recessive inheritance. Hemophilia is the most common congenital hemorrhagic disease.