Natural killer (NK) cells are essential components of the innate immune system, characterized by their ability to identify and eliminate abnormal cells through receptors that operate independently of major histocompatibility complex (MHC) restriction. As a result, NK cells play a critical role in anti-tumor, antiviral, and immune regulatory responses. Chimeric antigen receptor NK cell therapy (CAR-NK) enhances the targeting specificity and functional activity of NK cells, thereby augmenting their cytotoxic potential and opening new avenues for cancer treatment. To date, numerous clinical trials have evaluated NK cell therapy for anti-tumor, antiviral, and autoimmune diseases. This article summarizes the current research status of NK cell therapy in clinical applications, highlighting its promising efficacy and safety as an innovative immunotherapy. Despite challenges such as limited cell persistence and tumor microenvironment suppression, the prospects for further development in this field remain promising.