Objective To observe the mechanism of traumatic brain injury (TBI) following fluid percussion in rats. Methods TBI was made by the fluid percussion device. The intracellular free calcium concentrations([Ca2+ ] i) of hippocampus in the TBI was detected by flouormeter with fluorchrome Fura - 2/ AM. Results [Ca2+ ]i was increased markedly with moderate TBI. Conclusion The calcium channel of cell membrane was open after TBI which could cause a large mount of calcium into cell inner, and increased concentration of intracellular free calcium. It might play an important role in the experimental brain injury.