Natural killer (NK) cells are the main immune cells at the maternal-fetal interface and accumulate in the uterine decidua in early pregnancy. Many studies have shown that NK cells at the maternal-fetal interface have unique phenotypes and play critical roles in various processes, including immune tolerance during pregnancy, decidualization, invasion of trophoblasts, remodeling of the uterine spiral artery, formation of the placenta and growth of embryo. However, specific functions of NK cells and their mechanism remain to be fully elucidated. This review summarizes the research progress of NK cells at the maternal-fetal interface and their roles in the pregnancy-related disorders in recent years. The aims of this review are to gain deep insight of the function of NK cells at the maternal-fetal interface and provide new ideas for intervention of pregnancy-related diseases.