The mechanism of hemolysis reaction between type A and type O blood is the antigen-antibody reaction, and there is no A antigen or B antigen on the red blood cell membrane of type O blood, but there are anti-A and anti-B antibodies in the serum, while type A blood contains A antigen on the red blood cell membrane and anti-B antibodies in the serum. The patient will have a series of symptoms of hemolysis, such as anemia, yellow sclera, and in severe cases, enlarged liver and spleen, as well as acute hemolysis, such as chills, chills, back pain, hemoglobinuria, and even acute renal failure. Therefore, hemolytic reactions can occur between blood type A and blood type O. This is also the reason why homotypic blood transfusion is the principle in clinical practice.