Protein arginine methyltransferase 5 (PRMT5) exhibits elevated expression levels in a variety of cancers and has emerged as a critical target for cancer therapy in recent years. However, first-generation PRMT5 inhibitors have exhibited inadequate selectivity, leading to significant hematological toxicity, thus limiting their clinical utility. The second-generation PRMT5 inhibitors have shown marked improvement in safety and efficacy by selectively targeting MTAP-null tumor cells without impacting normal cells. This review systematically summarizes the biological and functional roles of PRMT5 in MTAP-deficient tumor cells, and comprehensively analyzes the research and development process, molecular binding mechanisms, and the latest advancements in clinical trials of the five second-generation PRMT5 inhibitors currently under investigation, aiming to provide valuable insights for further in-depth studies in this field.