Blood type is detected by the principle of antigen-antibody reaction. People with different blood types contain different antigens on the surface of red blood cells, which can react with the corresponding antibodies and appear as agglutination reactions visible to the naked eye. The blood type test is performed by taking human peripheral blood, dropping it on two slides, and then dripping it with the liquid of anti-A serum and anti-B serum respectively, and observing with the naked eye whether agglutination appears. If an agglutination appears, it indicates a positive reaction. If a person’s blood type reacts only with the anti-A serum, then the blood type is A blood. If it reacts only with anti-B serum the blood type is B. If it reacts with both anti-A and anti-B antibody sera, then the blood type is AB. If there is no agglutination with either the anti-A antibody or anti-B antibody serum, then the blood type is O.