Human leukocyte antigen (HLA), the major human histocompatibility complex, has a very important biological function as a marker for mutual recognition of different individual immune cells. HLA antigen is encoded by a set of genes located on chromosome 6 and is mainly expressed on the surface of nucleated cell membranes, especially in human leukocyte membranes which are rich in HLA molecules, hence the name human leukocyte antigen. Because HLA reflects the degree of histocompatibility between the recipient of an organ transplant and the donor providing the transplanted organ, and is closely related to rejection after organ transplantation, HLA is also called transplant antigen. The most closely related to organ transplant rejection is known to be the A and B loci of HLA class I antigens and the DR loci of HLA class II antigens, each of which has two antigens expressed, one from the father’s gene and one from the mother’s gene. Therefore, before transplantation, it is necessary to test the six antigens of HLA-A, B and DR loci on the lymphocyte membrane in the peripheral blood of the transplant recipient and donor, and select the recipient and donor with the most compatible HLA for transplantation according to the test results. A large number of clinical studies at home and abroad have shown that the higher the degree of HLA compatibility between the recipient and the donor, that is, the higher the number of identical antigens among the six HLA-A, B and DR antigens between the recipient and the donor, the lower the incidence of rejection, and the higher the transplantation success rate and long-term survival rate of the transplanted organ. Conversely, the more likely it is that rejection will occur, thereby reducing graft success and graft survival. A statistical analysis of more than 50,000 kidney transplant follow-up cases by the National Network for Organ Sharing (UNOS) showed that there was a 20% and 30% difference between the 3-year and 10-year survival rates of transplanted kidneys with identical (matched) and different (mismatched) HLA-A, B, and DR antigens between recipients and donors, and a 25% difference in the incidence of acute rejection. Therefore, a good HLA match between recipient and donor is of great clinical importance to reduce rejection and prolong functional graft survival after surgery.