Microglia are the immune cells in central neural system. Microglia play an important role in central neural system such as surrounding environment monitoring, apoptosis induction and mature synapse formation. Besides, as a pathological process, traumatic brain injury (TBI) can cause the structure and function damage of central nervous system. While the activated microglia can change the TBI-induced pathological process and play an important role during the course of injury. Therefore, the authors review the important physiological function of microglia and its pathological role so as to provide references for clinical treatment.