Aim To study the pathological changes of and relationship between secondary brain swelling and brain edema following acute brain injury. Methods The pathological changes at different time points (6,24,72 hour and 7 day) and the brain water content were measured under the light and electric microscope on the model of brain injury of Guinea pig and tested at every time phase. Results Brain swelling appeared at 6 hour after brain injury, and reached peak at 24 hour then decreased gradually. Brain edema appeared obviously at 24 hour after brain injury, reached peak at 72 hour and one week later it gradually dropped. Conclusion Brain swelling appears earlier than brain edema after brain injury, and they can coexist.