To solve the problem of structure strength caused by rocket-assisted equipment entering into water at high speed, the finite element model was established using the finite element software Ansys/Ls-dyna in this paper. The simulation of structure response to highspeed water entry was studied with ALE muti-material group algorithm using the plastic_kinematic nonlinear model for shell material and the gruneisen equation of state for water and air material. The simulation result shows that the head structure will be damaged when impact on the water. Considering the limit of internal space, the method of adding the internal supporter without changing the thickness was used to reinforce the shell strength. Through the analysis, the optimized structure strength is improved obviously to meet the design requirement and provide reference for the anti-impact design of the projectile.