Abstract: Aiming at the problem that the structure damage and trajectory out of control may be caused by the huge impact load when the vehicle enters the water at a high speed of more than 100 m/s, and the load reduction capacity of the existing buffer measures is limited, a gradient density buffer head cap for the vehicle entering the water at a high speed is designed in this paper to ensure that the vehicle can enter the water safely at a high speed, and the detailed design process is given. At the same time, based on the ALE (arbitrary Lagrangian-Eulerian) algorithm, a numerical calculation model of high-speed water entry of the vehicle with a buffer head cap is established, and the results of numerical calculation are in good agreement with the experimental data. Then, on this basis, the numerical research on the characteristics of high-speed water entry and load reduction of the vehicle with gradient density buffer head cap is carried out, and the influence laws of important parameters such as different layer thickness, positive and negative density gradient arrangement and interlayer density difference of the double-layer buffer on the energy absorption and load reduction effect of the buffer head cap are explored, and the large-scale model high-speed water entry impact test is carried out, The test data are filtered according to the natural frequency of the second-order bending mode in the dry modal analysis of the vehicle model. The results show that in the range studied in this paper, the layered buffer shows a stronger impact energy absorption effect than the non layered buffer, and the impact energy absorbed by the buffer increases with the increase of the number of layers; The buffer with negative density gradient is better than that with positive density gradient; The greater the density difference between layers, the greater the loss of impact energy, and the better the load reduction effect of buffer head cap.