Abstract: Head collisions can induce Traumatic Brain Injury (TBI), and the brain contusion is the most common one with high lethality and high disability rate. Based on the numerical simulation method, studies are carrid out to reveal the mechanism of the brain contusion in this paper, which is of great significance for prevention and treatment of this brain injury as well as development of protective equipments. Firstly, a three-dimensional (3D) numerical head model is established based on Magnetic Resonance Imaging (MRI) of the human head with physiological characteristics and detailed structures. In this model, the skull is characterized by the typical sandwich structure. The inner and outer layers are compact bone with higher rigidity and density, while the middle layer is spongy bone with less rigidity and density. In order to simulate the interaction between the brain and the skull, the Cerebrospinal Fluid (CSF) and the arachnoid trabeculae are simplified as one substance. The state equation is used to characterize the liquid properties of CSF, and a small shear modulus is considered for the shear transfer of the arachnoid trabecula. Then, the validity of the numerical head model is verified based on the forehead collision of a dead body. The numerical model adopts three different boundary conditions of the neck to simulate this forehead collision, namely the free boundary, vertical boundary and fixed boundary condition. Simulation results for the free boundary are in good agreement with experimental data, illustrating the validity of the numerical head model for head collisions. On the contrary, the vertical or fixed boundary condition leads to large deviation from experimental results, because these two boundaries are over constraint resulting in alternations of positive and negative intracranial pressures at the impact and opposite positions. Finally, the numerical head model verified above is used to simulate the head impact at the occiput. Thus, simulation results for the forehead collision and occiput collision are obtained. The analyses are carried out on dynamic rules of the brain pressure (volume deformation) and Mises stress (shear deformation). By combining dynamic rules with statistical clinical data of TBI, the damage mechanism of brain contusion is revealed and the corresponding criterion is established.