NK cells, also known as natural killer cells, belong to lymphocytes and are also a type of human immune cells. the role of NK cells is manifested in the following aspects: firstly, NK cells have an anti-viral effect and can produce cytokines, interleukins and interferons without antigen stimulation when their organism is infected by viruses to fight against tumor development and viral infections. Secondly, they play a good surveillance role in tumors and will monitor the human immune lifespan and the damage of tumor cells, etc. Third, NK cells can mediate human immune function and prevent the generation of autoimmune diseases and other abnormalities of immune function. Therefore, by testing the function of NK cells in clinical practice, it is possible to understand the immune status of patients, so that a comprehensive analysis can be made to determine whether the patients are suffering from diseases such as hypo-immune function, hyper-immune function and immunoproliferative diseases.