Natural killer (NK) cells are pivotal effectors in innate antitumor immunity by mediating cytotoxicity, secreting cytokines, or expressing cell membrane receptors, which facilitate interactions with other immune cells. The cytotoxic activity and immune function of NK cells are governed by dynamic receptor-ligand interactions, cytokine networks, and metabolic-epigenetic crosstalk within the tumor microenvironment (TME). Recent years, NK cell-based therapies are emerging as a promising clinical approach for antitumor treatment, owing to their rapid response, unique recognition mechanisms, potent cytotoxic capabilities, and memory-like characteristics, along with their low risk of posttreatment adverse effects and cost effectiveness. However, immunosuppression and metabolic reprogramming driven by TME subvert NK cell surveillance, impairing its antitumor function. This review comprehensively details molecular mechanisms underpinning NK cell dysfunction, including dysregulated activating/inhibitory receptor signaling, metabolic reprogramming, and epigenetic silencing of effector genes. We further synthesize advances in clinical strategies to restore NK cytotoxicity including ex vivo expansion for adoptive transfer, chimeric antigen receptor-NK engineering, TME-remodeling agents, immune checkpoint blockade, cytokine-based therapies, and NK cell engagers targeting tumor antigens. By bridging mechanistic insights with translational applications, this work provides a framework for rationally designed NK cell-based immunotherapies to overcome resistance across solid and hematologic malignancies.© 2025 The Author(s). MedComm published by Sichuan International Medical Exchange & Promotion Association (SCIMEA) and John Wiley & Sons Australia, Ltd.