Abstract: The Z-direction lattice reinforced foam sandwich composite material retains the high specific stiffness and strength of the traditional sandwich structure, and greatly improves its Z-direction mechanical properties. At the same time, it has good structural and functional designability to meet the needs of some special extreme conditions. In this paper, the underwater performance of the Z-direction reinforced foam sandwich composite under hydrostatic pressure is experimentally investigated, and the Z-direction deformation and in-plane stress under different pressures are obtained. And based on ABAQUS finite element software, the test simulation model of a Z-direction lattice reinforced foam sandwich composite material under hydrostatic pressure is established, its mechanical behavior is simulated and analyzed from the perspective of finite element, and the force situation of the lattice predicted. The simulation results are similar to that of the experiment, verifying the rationality and reliability of the finite element model, and laying the foundation for the engineering simulation design of materials of this kind.