Only type O blood can be transfused to type O blood. The principle of blood transfusion is to transfuse blood of the same type. 1. Human blood types are broadly categorized into A, B, AB and O. These four blood types can also be categorized into RH-positive, RH-negative and so on. 2. Type A blood cells contain A antigens, type B blood cells contain B antigens, type AB blood cells contain AB antigens, and blood cells with no A or B antigens are called type O blood. 3. Because type O blood contains neither A nor B antigens, it is not acceptable to receive transfusions of type A, B, or AB, or it will lead to different degrees of hemolysis. 4. It should also be noted that when transfusing blood, one should also pay attention to whether it is RH-positive or RH-negative, and RH-negative donors’ blood cannot be transfused to RH-positive recipients. It is recommended to go to regular hospitals for blood transfusion after cross-matching to avoid serious complications.