Abstract: When dropping into water from the air, large cylinder shell structures may suffer larger deformation or collapse due to the strong water impact. To improve the structural crashworthiness, the simulation was done, combined with corresponding experiments. Through the static tensile and dynamic SHPB tests, the nonlinear constitutive relationships of alternative materials were obtained, and the corresponding plastic-kinematic material models were built. Simplified models scaled 1∶ 10 were dropped into water for test, and their simulation was done also. Full sized structure in detail and partial fluid domain were modeled, composed by thin-shell, water and air. Based on the ALE/Lagrange penalty function coupling algorithm without erosion, the process dropping into water was simulated by finite element method(FEM). Then the weakness of original design was found, and an improved scheme was proposed and verified by simulation. The proposed approach is also applicable for other fluid impact problems related to large deformation and nonlinear.