Abstract: Epoxy resin-based buoyancy materials have broad application prospects in marine structures due to their low density, high strength, and functional designability. However, their safety has not been fully discussed, and there is a lack of relevant research on the failure criteria of buoyancy materials under ultimate load. Quasi-static uniaxial tensile/compressive and dynamic uniaxial compressive experiments were carried out to analyze the failure modes of buoyancy materials under simple stress states, and the strain-rate constitutive model of epoxy resin-based buoyancy materials was fitted. Based on the experimental observation results, using the pressure-shear coupling Mohr-Coulomb theory, a user-defined material subroutine (VUMAT) was compiled and implemented in the finite element method. The results show that there is a tension-compression difference in epoxy resin-based buoyancy materials, and the compressive strength is significantly higher than the tensile strength. The uniaxial compression failure mode of buoyancy materials is mainly divided into conical fragments on the upper surface and lateral splitting fragments. Buoyancy materials have a strain-rate effect, mainly manifested as an increase in strength with an increase in strain-rate. The failure criterion proposed in this paper can simulate the experimental results of buoyancy materials.