By using the rigid–fluid impact model and the resultant force direction expansion hypothesis of soil deformation, the relation between the resultant force of infinitesimal and the velocity of soil infinitesimal is established. On this basis, the dynamics equations of the rod are established when half-infinite soil is penetrated by a long rod. The impact force history curves and the penetration displacement history curves are determined by the numerical of the nonlinear equations. It is obtained that with the increase of initial angle velocity, the penetration displacement will increase.