The structure entering water is a typical fluid-solid coupling problem and the process is complex. For three-dimensional elastic structures, experiments and numerical simulation are the main research methods. In order to analyze the water entry load of the helicopter box segment, the vertical water entry impact test is carried out, and the FEM-SPH coupling numerical method is applied to simulation analysis. The overload, pressure and strain results under different material configurations and speeds are calculated and compared with the test results. It shows that the simulation results are in good agreement with the test values, and the predicted structural failure mode and deformation are basically consistent with the test results, which can be used as a reference for the structural design of real helicopter water entry impact.