As the most vulnerable part of the aircraft, the fuel tank is damaged by hydrodynamics ram effect when attacked by high-speed projectiles, which will directly threaten the safety of the aircraft. The numerical research on the hydrodynamics ram effect is of great significance. In this paper, CEL method is used to simulate the hydrodynamics ram effect. Firstly, the accuracy of the numerical model is verified by comparing with the existing experimental results; Then, the effects of impact velocity and liquid filling rate on the hydrodynamics ram effect are analyzed. In order to reduce the damage power of hydrodynamics ram effect, the design of protective structure is numerically analyzed. The results show that the damage power of hydrodynamics ram effect comes from shock wave. The greater the kinetic energy of projectile and the higher the liquid filling rate, the greater the damage of oil tank. The protective baffle can reduce the damage caused by shock wave to the oil tank structure to a certain extent, and the air-interlayer protective structure is the best for the protective effect.