The blood type is determined by the antigens on the surface of red blood cells, and the most common blood group systems in clinical practice include the ABO blood group system and the Rh blood group system. For most ethnic minorities and more than 99% of Han Chinese population, Rh blood group is positive. Rh blood group is the most complex blood group system among human beings, with dozens of antigens, D antigen is the strongest antigen, so people with D antigen are called RhD positive, so RhD+ means RhD blood group positive.