F9 KO mice are Hemophilia B disease models constructed by knocking out the mouse F9 gene. F9 KO mice lack F9 mRNA expression and exhibit coagulation dysfunction and other Hemophilia B-related phenotypes. They can be used to study the genetic mechanisms and clinical phenotypes of Hemophilia B in humans and to assist in developing, screening, and evaluating therapeutic drugs. The homozygotes are viable and fertile. Tail docking may lead to significant bleeding. Immediate hemostasis, such as cauterizing the tail incision, is advised to prevent health complications in homozygous mice.