In the past, people called O blood as universal blood and universal transfusion because there is no A antigen and no B antigen on the red blood cell membrane of O blood. When transfusing blood to a patient, the red blood cell membrane of the donor will not produce agglutination reaction with the antibody in the recipient’s serum because there is no A antigen and B antigen. With the development of modern medicine, we know that clinical blood transfusion is based on the principle of homozygous blood, and O blood is not universal blood. Only in emergency situations when there is no other blood type can O blood be slowly transfused to the patient in small amounts, with the purpose of saving the patient’s life, if there is homozygous blood or the principle of transfusion of homozygous blood. In the past, AB blood type was called the universal recipient, but in fact, AB blood type is not the universal recipient.