Abstract: In recent years, the science and technology of organ transplantation have developed rapidly, which has been widely applied worldwide. However, multiple challenges remain to be resolved by clinicians, such as functional damage and immune rejection of transplant organs, immune deficiency caused by extensive use of immunosuppressants, chronic allograft dysfunction and adverse reactions. This article introduced relevant key research results published in 2021, taking the function and mechanism of immune cell subsets in the process of organ transplantation rejection or immune tolerance, and the research and application of new materials and drugs in organ transplantation as the main clues. The latest research progresses on regional immune response, especially the application of tissue-resident memory T cell in organ transplantation, were briefly summarized, and the future development of transplantation immunology was prospected.