Blood group RH means RH blood group, just like ABO blood group system, RH blood group is also a kind of blood group system in human body.RH is the abbreviation of Indian rhesus monkey, because this blood group was first found on the red blood cell membrane from Indian rhesus monkey, later RH blood group was also found on the red blood cell membrane in human.RH blood group is divided into two kinds according to whether the red blood cell membrane contains D antigen, those containing D antigen are RH-positive, without D antigen is RH-negative, the antigenic nature of D antigen is stronger, so that RH-negative people will produce the corresponding antibodies after contact with D antigen, the second contact with D antigen will occur when the obvious antigen-antibody reaction, resulting in hemolysis. Therefore, RH-negative people can receive RH-positive blood for the first transfusion in the clinical transfusion, but they can only receive RH-negative blood for the second transfusion, and if RH-positive blood is transfused, a serious hemolytic reaction will occur.