Natural killer (NK) cells are key innate immune cells that provide the first line of defense against viral infection and cancer. Although NK cells can discriminate between ″self″ and ″non-self,″ recognize abnormal cells, and eliminate transformed cells and malignancies in real time, tumors develop several strategies to escape from NK cell attack. These strategies include upregulating ligands for the inhibitory receptors of NK cells and producing soluble molecules or immunosuppressive factors. Various types of NK cells are currently being applied in clinical trials, including autologous or allogeneic NK cells, umbilical cord blood (UCB) or induced pluripotent stem cell (iPSC)-derived NK cells, memory-like NK cells, and NK cell line NK-92 cells, for the treatment of different types of tumors. Chimeric antigen receptors (CARs)-NK cells have recently shown great potential due to their redirect specificity and effective antitumor activity. In this review, we summarize the mechanisms of tumor escape from NK cell recognition, the current status and advanced progress of NK cell-based immunotherapy, ways of enhancing the antitumor capacity of NK cells in vivo, and major challenges for clinical practice in this field.