Triggering receptor expressed on myeloid cells 2 (TREM2) is a receptor specifically expressed on the surface of microglia. It maintains the homeostasis of the neuroimmune microenvironment by regulating microglia proliferation, activation, and phagocytosis. Numerous studies have demonstrated that in Alzheimer's disease and Parkinson's disease, TREM2 primarily promotes M2-type microglial polarization via the DAP10/12 or PLCγ2 pathway, enhances microglial phagocytic function and alleviating oxidative stress and neuroinflammation. In epilepsy and stroke, TREM2 regulates the transformation of microglia into disease-associated microglia by activating the PI3K or Wnt pathway, thereby reducing neuroinflammation and facilating tissue repair. These findings suggest that TREM2 plays a crucial role in the pathological progress of the aforementioned neurodegenerative diseases; however, its underlying mechanisms and clinical significance remain inadequately characterized. Therefore, this review systematically and comprehensively summarizes the biological characteristics, pathophysiological functions, and potential mechanisms of TREM2, aiming to provide a reliable theoretical foundation for TREM2 and its associated signaling pathways as candidate targets for the clinical diagnosis and treatment of central nervous system diseases.