Objective To discuss the mechanism of progesterone that soften brain water content in traumatic brain edema in rats. Methods The models of focal lobe contusion and laceration of brain were made on the male rats treated by the progesterone following injury. Immunohistochemical method was used to assess the expression of aquaporin-4 (AQP4). Evan's Blue method was used to detect the permeability of blood-brain barrier. Results Treated by the progesteron, the brain water content was significantly decreased, and the lower expression of AQP4 took place on astrocytes of the contusion and peri-contusion of the brain tissue after 24 h,72h ,and 120h . The content of EB was decreased at 6 h and 24 h post-injury. Conclusions Progesterone can soften the traumatic brain water content, which may be associated with the attenuation of AQP4 in frontal lobe contusion following traumatic brain injury ( TBI) and progesterone can protect the blood-brain barrier at early time after TBI.