The abo blood group is the most widely used blood group in clinical practice. There is only agglutinin on the surface of red blood cells, i.e. blood type A. There is only B agglutinin on the erythrocyte membrane, i.e., B blood type. There is neither A nor B aggrecan on the red blood cell membrane, which is O blood type. There are both A-type aggrecan and B-type aggrecan on the red cell membrane, i.e., AB blood type. 1. Blood type A: If only one kind of agglutinin is found on the surface of the subject’s erythrocytes in the red blood cell examination, and only anti-B-type agglutinin is found in the serum, then it is type A blood. 2. Blood type B: If only B-type agglutinin is found on the erythrocyte membrane and only anti-A-type agglutinin is found in the serum, it is blood type B. 3. Blood type O: If there is neither A-type agglutinin nor B-type agglutinin on the red cell membrane of the subject, and there is both anti-A-type agglutinin and B-type agglutinin in the serum, then it belongs to type O blood. 4. AB blood type: this blood type is opposite to O blood type. In the process of examination, it will be found that the subject’s erythrocyte membrane at the same time the existence of A and B agglutinin, there is no anti-A and B agglutinin in the serum, then belongs to the AB blood type. Specific blood group identification should be done under the supervision of a physician.