Functional near infrared spectroscopy (fNIRS) technology is utilized to monitor brain tissue of rat model of traumatic brain injury (TBI). The reduced scattering coefficient of the local cortex of rats is monitored and recorded in vivo and real time by the fNIRS system. Brain water content (BWC) is measured by the wet and dry weight method. Intracranial pressure (ICP) is measured invasive ICP monitor. Imaging data of rat model is detected by small animal magnetic resonance imaging (MRI). Experimental results show that, there exists positive correlation between parameters and BWC, and ICP, the occurrence and development of cerebral edema can be detected earlier with the sensitive indicator of scattering coefficient.